diff --git a/.gitignore b/.gitignore
index 657a0dd..fd8c240 100644
--- a/.gitignore
+++ b/.gitignore
@@ -12,6 +12,8 @@ test/test_materials
 test/test_spheres
 test/test_world
 test/test_camera
+test/test_shapes
+test/test_planes
 raytracer
 *.ppm
 *.png
diff --git a/intersections.h b/intersections.h
index d4185ab..b93ab63 100644
--- a/intersections.h
+++ b/intersections.h
@@ -1,29 +1,26 @@
 #pragma once
 
 #include <stdarg.h>
-#include <assert.h>
-#include <stdbool.h>
-
-#include "spheres.h"
-#include "rays.h"
 
 struct intersection {
   float t;
-  struct sphere const * object;
+  struct shape const * object;
 };
 
-struct intersection intersection(float t, struct sphere const * const object)
-{
-  return (struct intersection){ t, object };
-}
-
-#define MAX_INTERSECTIONS 1024
+#ifndef INTERSECTIONS_MAX
+#define INTERSECTIONS_MAX 1024
+#endif
 
 struct intersections {
   int count;
-  struct intersection i[MAX_INTERSECTIONS];
+  struct intersection i[INTERSECTIONS_MAX];
 };
 
+struct intersection intersection(float t, struct shape const * const object)
+{
+  return (struct intersection){ t, object };
+}
+
 inline static void intersections(struct intersections * intersections, int count, ...)
 {
   va_list ap;
@@ -35,113 +32,3 @@ inline static void intersections(struct intersections * intersections, int count
 
   intersections->count = count;
 }
-
-inline static void intersect(struct sphere const * const s, struct ray r, struct intersections * intersections)
-{
-  struct mat4x4 m = mat4x4_inverse(&s->transform);
-  struct ray r2 = ray_transform(r, &m);
-  struct tuple sphere_to_ray = tuple_sub(r2.origin, point(0.0f, 0.0f, 0.0f));
-
-  float a = tuple_dot(r2.direction, r2.direction);
-  float b = 2 * tuple_dot(r2.direction, sphere_to_ray);
-  float c = tuple_dot(sphere_to_ray, sphere_to_ray) - 1;
-
-  float discriminant = b * b - 4 * a * c;
-
-  if (discriminant < 0) {
-    return;
-  } else {
-    float root = sqrtf(discriminant);
-    float t1 = (-b - root) / (2 * a);
-    float t2 = (-b + root) / (2 * a);
-
-    intersections->i[intersections->count++] = intersection(t1, s);
-    intersections->i[intersections->count++] = intersection(t2, s);
-    assert(intersections->count < MAX_INTERSECTIONS);
-    return;
-  }
-}
-
-inline static struct intersection * hit(struct intersections * xs)
-{
-  struct intersection * i = NULL;
-  for (int n = 0; n < xs->count; n++) {
-    if (xs->i[n].t >= 0) {
-      if (i == NULL || i->t > xs->i[n].t)
-        i = &xs->i[n];
-    }
-  }
-  return i;
-}
-
-
-inline static void intersections_sort(struct intersections * xs)
-{
-#define left_child(i) (2 * i + 1)
-
-  int start = xs->count / 2;
-  int end = xs->count;
-  while (end > 1) {
-    if (start > 0) {
-      start = start - 1;
-    } else {
-      end = end - 1;
-      struct intersection tmp = xs->i[0];
-      xs->i[0] = xs->i[end];
-      xs->i[end] = tmp;
-    }
-
-    int root = start;
-    while (left_child(root) < end) {
-      int child = left_child(root);
-      if (child + 1 < end && xs->i[child].t < xs->i[child+1].t) {
-        child = child + 1;
-      }
-      if (xs->i[root].t < xs->i[child].t) {
-        struct intersection tmp = xs->i[root];
-        xs->i[root] = xs->i[child];
-        xs->i[child] = tmp;
-        root = child;
-      } else {
-        break;
-      }
-    }
-  }
-
-#undef left_child
-}
-
-struct computations {
-  float t;
-  struct sphere const * object;
-  struct tuple point;
-  struct tuple eyev;
-  struct tuple normalv;
-  bool inside;
-  struct tuple over_point;
-};
-
-inline static struct computations prepare_computations(struct intersection intersection, struct ray ray)
-{
-  struct tuple point = ray_position(ray, intersection.t);
-  struct tuple eyev = tuple_neg(ray.direction);
-  struct tuple normalv = sphere_normal_at(intersection.object, point);
-
-  bool inside = false;
-  if (tuple_dot(normalv, eyev) < 0.0f) {
-    inside = true;
-    normalv = tuple_neg(normalv);
-  }
-
-  struct tuple over_point = tuple_add(point, tuple_mul(normalv, epsilon * 100));
-
-  return (struct computations){
-    intersection.t,
-    intersection.object,
-    point,
-    eyev,
-    normalv,
-    inside,
-    over_point
-  };
-}
diff --git a/intersections_shapes.h b/intersections_shapes.h
new file mode 100644
index 0000000..c2c00d5
--- /dev/null
+++ b/intersections_shapes.h
@@ -0,0 +1,153 @@
+#pragma once
+
+#include <assert.h>
+#include <stdbool.h>
+
+#include "rays.h"
+#include "shapes.h"
+#include "intersections.h"
+#include "spheres.h"
+#include "planes.h"
+
+#ifdef TEST
+struct ray intersections_saved_ray;
+#endif
+
+inline static void intersect(struct shape const * const s, struct ray r, struct intersections * intersections)
+{
+  struct mat4x4 m = mat4x4_inverse(&s->transform);
+  struct ray local_ray = ray_transform(r, &m);
+
+  switch (s->type) {
+#ifdef TEST
+  case SHAPE_TEST:
+    intersections_saved_ray = local_ray;
+    break;
+#endif
+  case SHAPE_SPHERE:
+    sphere_intersect(s, local_ray, intersections);
+    break;
+  case SHAPE_PLANE:
+    plane_intersect(s, local_ray, intersections);
+    break;
+  default:
+    assert(false);
+    break;
+  }
+  assert(intersections->count < INTERSECTIONS_MAX);
+}
+
+inline static struct intersection * hit(struct intersections * xs)
+{
+  struct intersection * i = NULL;
+  for (int n = 0; n < xs->count; n++) {
+    if (xs->i[n].t >= 0) {
+      if (i == NULL || i->t > xs->i[n].t)
+        i = &xs->i[n];
+    }
+  }
+  return i;
+}
+
+
+inline static void intersections_sort(struct intersections * xs)
+{
+#define left_child(i) (2 * i + 1)
+
+  int start = xs->count / 2;
+  int end = xs->count;
+  while (end > 1) {
+    if (start > 0) {
+      start = start - 1;
+    } else {
+      end = end - 1;
+      struct intersection tmp = xs->i[0];
+      xs->i[0] = xs->i[end];
+      xs->i[end] = tmp;
+    }
+
+    int root = start;
+    while (left_child(root) < end) {
+      int child = left_child(root);
+      if (child + 1 < end && xs->i[child].t < xs->i[child+1].t) {
+        child = child + 1;
+      }
+      if (xs->i[root].t < xs->i[child].t) {
+        struct intersection tmp = xs->i[root];
+        xs->i[root] = xs->i[child];
+        xs->i[child] = tmp;
+        root = child;
+      } else {
+        break;
+      }
+    }
+  }
+
+#undef left_child
+}
+
+struct computations {
+  float t;
+  struct shape const * object;
+  struct tuple point;
+  struct tuple eyev;
+  struct tuple normalv;
+  bool inside;
+  struct tuple over_point;
+};
+
+inline static struct tuple normal_at(struct shape const * const s, struct tuple world_point)
+{
+  struct mat4x4 inv = mat4x4_inverse(&s->transform);
+  struct mat4x4 inv_t = mat4x4_transpose(&inv);
+
+  struct tuple local_point = mat4x4_mul_t(&inv, &world_point);
+  struct tuple local_normal;
+
+  switch (s->type) {
+#ifdef TEST
+  case SHAPE_TEST:
+    local_normal = vector(local_point.x, local_point.y, local_point.z);
+    break;
+#endif
+  case SHAPE_SPHERE:
+    local_normal = sphere_normal_at(local_point);
+    break;
+  case SHAPE_PLANE:
+    local_normal = plane_normal_at(local_point);
+    break;
+  default:
+    assert(false);
+    break;
+  }
+
+  struct tuple world_normal = mat4x4_mul_t(&inv_t, &local_normal);
+  world_normal.w = 0.0f;
+
+  return tuple_normalize(world_normal);
+}
+
+inline static struct computations prepare_computations(struct intersection intersection, struct ray ray)
+{
+  struct tuple point = ray_position(ray, intersection.t);
+  struct tuple eyev = tuple_neg(ray.direction);
+  struct tuple normalv = normal_at(intersection.object, point);
+
+  bool inside = false;
+  if (tuple_dot(normalv, eyev) < 0.0f) {
+    inside = true;
+    normalv = tuple_neg(normalv);
+  }
+
+  struct tuple over_point = tuple_add(point, tuple_mul(normalv, epsilon * 100));
+
+  return (struct computations){
+    intersection.t,
+    intersection.object,
+    point,
+    eyev,
+    normalv,
+    inside,
+    over_point
+  };
+}
diff --git a/math.h b/math.h
index 166cd90..698e9d0 100644
--- a/math.h
+++ b/math.h
@@ -6,6 +6,7 @@
 #define sinf __builtin_sinf
 #define powf __builtin_powf
 #define tanf __builtin_tanf
+#define fabsf __builtin_fabsf
 
 static const float tau = 6.283185307179586f;
 static const float pi = tau / 2.0f;
diff --git a/planes.h b/planes.h
new file mode 100644
index 0000000..cfefecc
--- /dev/null
+++ b/planes.h
@@ -0,0 +1,35 @@
+#pragma once
+
+#include "math.h"
+#include "matrices.h"
+#include "materials.h"
+#include "shapes.h"
+#include "rays.h"
+#include "intersections.h"
+
+inline static struct shape plane()
+{
+  return (struct shape){
+    mat4x4_identity(),
+    material(),
+    SHAPE_PLANE,
+  };
+}
+
+inline static struct tuple plane_normal_at(struct tuple local_point)
+{
+  return vector(0.0f, 1.0f, 0.0f);
+}
+
+inline static void plane_intersect(struct shape const * const s, struct ray local_ray, struct intersections * intersections)
+{
+  if (fabsf(local_ray.direction.y) < epsilon) {
+    return;
+  }
+
+  float t = -local_ray.origin.y / local_ray.direction.y;
+
+  intersections->i[intersections->count++] = intersection(t, s);
+
+  return;
+}
diff --git a/rays.h b/rays.h
index 7d814f2..b73f539 100644
--- a/rays.h
+++ b/rays.h
@@ -1,6 +1,5 @@
 #pragma once
 
-#include "spheres.h"
 #include "tuples.h"
 #include "matrices.h"
 
diff --git a/raytracer.c b/raytracer.c
index faaab52..a88bb4e 100644
--- a/raytracer.c
+++ b/raytracer.c
@@ -22,12 +22,12 @@ int main()
   float pixel_size = wall_size / (float)canvas_pixels;
   float half = wall_size / 2.0f;
 
-  struct sphere floor = sphere();
-  floor.transform = scaling(10.0f, 0.01f, 10.0f);
+  struct shape floor = plane();
   floor.material.color = color(1.0f, 0.9f, 0.9f);
   floor.material.specular = 0.0f;
 
-  struct sphere left_wall = sphere();
+  /*
+  struct shape left_wall = sphere();
   {
     struct mat4x4 _translation = translation(0.0f, 0.0f, 5.0f);
     struct mat4x4 _rotation_y = rotation_y(-pi / 4.0f);
@@ -42,7 +42,7 @@ int main()
   }
   left_wall.material = floor.material;
 
-  struct sphere right_wall = sphere();
+  struct shape right_wall = sphere();
   {
     struct mat4x4 _translation = translation(0.0f, 0.0f, 5.0f);
     struct mat4x4 _rotation_y = rotation_y(pi / 4.0f);
@@ -56,14 +56,15 @@ int main()
     right_wall.transform = t2;
   }
   right_wall.material = floor.material;
+  */
 
-  struct sphere middle = sphere();
+  struct shape middle = sphere();
   middle.transform = translation(-0.5f, 1.0f, 0.5f);
   middle.material.color = color((float)0xfc / 255.f , (float)0x6d / 255.f, (float)0x09 / 255.f);
   middle.material.diffuse = 0.7;
   middle.material.specular = 0.3;
 
-  struct sphere right = sphere();
+  struct shape right = sphere();
   struct mat4x4 right_t = translation(1.5f, 0.5f, -0.5f);
   struct mat4x4 right_s = scaling(0.5f, 0.5f, 0.5f);
   right.transform = mat4x4_mul_m(&right_t, &right_s);
@@ -71,7 +72,7 @@ int main()
   right.material.diffuse = 0.7;
   right.material.specular = 0.3;
 
-  struct sphere left = sphere();
+  struct shape left = sphere();
   struct mat4x4 left_t = translation(-1.5f, 0.33f, -0.75f);
   struct mat4x4 left_s = scaling(0.33f, 0.33f, 0.33f);
   left.transform = mat4x4_mul_m(&left_t, &left_s);
@@ -85,22 +86,20 @@ int main()
 
   struct world world;
   world.light = light;
-  world.object_count = 6;
+  world.object_count = 4;
   world.objects[0] = floor;
-  world.objects[1] = left_wall;
-  world.objects[2] = right_wall;
-  world.objects[3] = middle;
-  world.objects[4] = right;
-  world.objects[5] = left;
+  world.objects[1] = middle;
+  world.objects[2] = right;
+  world.objects[3] = left;
 
-  struct camera _camera = camera(1600.0f, 800.0f, pi / 3.0f);
+  struct camera _camera = camera(400.0f, 200.0f, pi / 3.0f);
   _camera.transform = view_transform(point(0.0f, 1.5f, -5.0f),
                                      point(0.0f, 1.0f, 0.0f),
                                      vector(0.0f, 1.0f, 0.0f));
 
-  struct mat4x4 middle_t = world.objects[3].transform;
+  struct mat4x4 middle_t = world.objects[1].transform;
 
-  for (int i = 0; i < 360; i++) {
+  for (int i = 10; i < 360; i++) {
 
     _camera.transform = view_transform(point(5.0f * cosf(pi / 360 * (float)i / 10),
                                              1.5f,
@@ -118,7 +117,7 @@ int main()
     struct mat4x4 middle_ry = rotation_y(tau / 360.f * (float)i);
     struct mat4x4 middle_r = mat4x4_mul_m(&middle_rz, &middle_ry);
     struct mat4x4 middle_transform = mat4x4_mul_m(&middle_r, &middle_s);
-    world.objects[3].transform = mat4x4_mul_m(&middle_t, &middle_transform);
+    world.objects[1].transform = mat4x4_mul_m(&middle_t, &middle_transform);
 
     camera_render(&_camera, &world, &_canvas);
 
diff --git a/shapes.h b/shapes.h
new file mode 100644
index 0000000..61a95d3
--- /dev/null
+++ b/shapes.h
@@ -0,0 +1,25 @@
+#pragma once
+
+#include "matrices.h"
+#include "materials.h"
+
+enum shape_type {
+  SHAPE_TEST,
+  SHAPE_SPHERE,
+  SHAPE_PLANE,
+};
+
+struct shape {
+  struct mat4x4 transform;
+  struct material material;
+  enum shape_type type;
+};
+
+inline static struct shape shape()
+{
+  return (struct shape){
+    mat4x4_identity(),
+    material(),
+    SHAPE_TEST,
+  };
+}
diff --git a/spheres.h b/spheres.h
index d912c29..4428c3d 100644
--- a/spheres.h
+++ b/spheres.h
@@ -2,27 +2,43 @@
 
 #include "matrices.h"
 #include "materials.h"
+#include "shapes.h"
+#include "rays.h"
+#include "intersections.h"
 
-struct sphere {
-  struct mat4x4 transform;
-  struct material material;
-};
-
-inline static struct sphere sphere()
+inline static struct shape sphere()
 {
-  return (struct sphere){
+  return (struct shape){
     mat4x4_identity(),
-    material()
+    material(),
+    SHAPE_SPHERE,
   };
 }
 
-inline static struct tuple sphere_normal_at(struct sphere const * const s, struct tuple world_point)
+inline static struct tuple sphere_normal_at(struct tuple local_point)
 {
-  struct mat4x4 inv = mat4x4_inverse(&s->transform);
-  struct tuple object_point = mat4x4_mul_t(&inv, &world_point);
-  struct tuple object_normal = tuple_sub(object_point, point(0.0f, 0.0f, 0.0f));
-  struct mat4x4 inv_t = mat4x4_transpose(&inv);
-  struct tuple world_normal = mat4x4_mul_t(&inv_t, &object_normal);
-  world_normal.w = 0.0f;
-  return tuple_normalize(world_normal);
+  return tuple_sub(local_point, point(0.0f, 0.0f, 0.0f));
+}
+
+inline static void sphere_intersect(struct shape const * const s, struct ray local_ray, struct intersections * intersections)
+{
+  struct tuple sphere_to_ray = tuple_sub(local_ray.origin, point(0.0f, 0.0f, 0.0f));
+
+  float a = tuple_dot(local_ray.direction, local_ray.direction);
+  float b = 2 * tuple_dot(local_ray.direction, sphere_to_ray);
+  float c = tuple_dot(sphere_to_ray, sphere_to_ray) - 1;
+
+  float discriminant = b * b - 4 * a * c;
+
+  if (discriminant < 0) {
+    return;
+  } else {
+    float root = sqrtf(discriminant);
+    float t1 = (-b - root) / (2 * a);
+    float t2 = (-b + root) / (2 * a);
+
+    intersections->i[intersections->count++] = intersection(t1, s);
+    intersections->i[intersections->count++] = intersection(t2, s);
+    return;
+  }
 }
diff --git a/test/run.sh b/test/run.sh
index ce50151..54db03e 100644
--- a/test/run.sh
+++ b/test/run.sh
@@ -2,10 +2,13 @@
 
 set -eux
 
-for name in tuples canvas matrices transformations rays intersections spheres lights materials world camera; do
+
+for name in tuples canvas matrices transformations rays intersections shapes spheres planes lights materials world camera; do
     gcc -g -gdwarf-5 \
         -Wall -Werror -Wfatal-errors \
+        -Wno-error=unused-variable \
         -I. \
+        -DTEST \
         test/test_${name}.c -o test/test_${name} -O0 -lm
     ./test/test_${name}
 done
diff --git a/test/test_intersections.c b/test/test_intersections.c
index 98025dd..a42ff2a 100644
--- a/test/test_intersections.c
+++ b/test/test_intersections.c
@@ -1,7 +1,7 @@
 #include <stdbool.h>
 #include <stdio.h>
 
-#include "intersections.h"
+#include "intersections_shapes.h"
 #include "transformations.h"
 #include "runner.h"
 
@@ -9,7 +9,7 @@ static bool intersections_test_0(const char ** scenario)
 {
   *scenario = "An intersection encapsulates t and object";
 
-  struct sphere s = sphere();
+  struct shape s = sphere();
   struct intersection i = intersection(3.5f, &s);
 
   return
@@ -21,7 +21,7 @@ static bool intersections_test_1(const char ** scenario)
 {
   *scenario = "Aggregating intersections";
 
-  struct sphere s = sphere();
+  struct shape s = sphere();
   struct intersection i1 = intersection(1.0f, &s);
   struct intersection i2 = intersection(2.0f, &s);
   struct intersections xs;
@@ -37,7 +37,7 @@ static bool intersections_test_2(const char ** scenario)
 {
   *scenario = "The hit, when all intersections have positive t";
 
-  struct sphere s = sphere();
+  struct shape s = sphere();
   struct intersection i1 = intersection(1.0f, &s);
   struct intersection i2 = intersection(2.0f, &s);
   struct intersections xs;
@@ -55,7 +55,7 @@ static bool intersections_test_3(const char ** scenario)
 {
   *scenario = "The hit, when some intersections have negative t";
 
-  struct sphere s = sphere();
+  struct shape s = sphere();
   struct intersection i1 = intersection(-1.0f, &s);
   struct intersection i2 = intersection( 1.0f, &s);
   struct intersections xs;
@@ -73,7 +73,7 @@ static bool intersections_test_4(const char ** scenario)
 {
   *scenario = "The hit, when all intersections have negative t";
 
-  struct sphere s = sphere();
+  struct shape s = sphere();
   struct intersection i1 = intersection(-2.0f, &s);
   struct intersection i2 = intersection(-1.0f, &s);
   struct intersections xs;
@@ -88,7 +88,7 @@ static bool intersections_test_5(const char ** scenario)
 {
   *scenario = "The hit is always the lowest nonnegative intersection";
 
-  struct sphere s = sphere();
+  struct shape s = sphere();
   struct intersection i1 = intersection( 5.0f, &s);
   struct intersection i2 = intersection( 7.0f, &s);
   struct intersection i3 = intersection(-3.0f, &s);
@@ -108,13 +108,13 @@ static bool intersections_test_6(const char ** scenario)
 {
   *scenario = "In-place ascending sort of intersections";
 
-  struct sphere s1 = sphere();
+  struct shape s1 = sphere();
   s1.material.ambient = 1.0f;
-  struct sphere s2 = sphere();
+  struct shape s2 = sphere();
   s2.material.ambient = 2.0f;
-  struct sphere s3 = sphere();
+  struct shape s3 = sphere();
   s3.material.ambient = 3.0f;
-  struct sphere s4 = sphere();
+  struct shape s4 = sphere();
   s4.material.ambient = 4.0f;
   struct intersection i1 = intersection( 5.0f, &s1);
   struct intersection i2 = intersection( 7.0f, &s2);
@@ -141,7 +141,7 @@ static bool intersections_test_7(const char ** scenario)
   *scenario = "Precomputing the state of an intersection";
 
   struct ray r = ray(point(0.0f, 0.0f, -5.0f), vector(0.0f, 0.0f, 1.0f));
-  struct sphere shape = sphere();
+  struct shape shape = sphere();
   struct intersection i = intersection(4.0f, &shape);
   struct computations comps = prepare_computations(i, r);
 
@@ -158,7 +158,7 @@ static bool intersections_test_8(const char ** scenario)
   *scenario = "The hit, when an intersection occurs on the outside";
 
   struct ray r = ray(point(0.0f, 0.0f, -5.0f), vector(0.0f, 0.0f, 1.0f));
-  struct sphere shape = sphere();
+  struct shape shape = sphere();
   struct intersection i = intersection(4.0f, &shape);
   struct computations comps = prepare_computations(i, r);
 
@@ -171,7 +171,7 @@ static bool intersections_test_9(const char ** scenario)
   *scenario = "The hit, when an intersection occurs on the inside";
 
   struct ray r = ray(point(0.0f, 0.0f, 0.0f), vector(0.0f, 0.0f, 1.0f));
-  struct sphere shape = sphere();
+  struct shape shape = sphere();
   struct intersection i = intersection(1.0f, &shape);
   struct computations comps = prepare_computations(i, r);
 
@@ -187,7 +187,7 @@ static bool intersections_test_10(const char ** scenario)
   *scenario = "The hit should offset the point";
 
   struct ray r = ray(point(0.0f, 0.0f, -5.0f), vector(0.0f, 0.0f, 1.0f));
-  struct sphere shape = sphere();
+  struct shape shape = sphere();
   shape.transform = translation(0.0f, 0.0f, 1.0f);
   struct intersection i = intersection(5.0f, &shape);
   struct computations comps = prepare_computations(i, r);
diff --git a/test/test_planes.c b/test/test_planes.c
new file mode 100644
index 0000000..79a6b5f
--- /dev/null
+++ b/test/test_planes.c
@@ -0,0 +1,87 @@
+#include <stdbool.h>
+#include <stdio.h>
+
+#include "rays.h"
+#include "planes.h"
+#include "intersections_shapes.h"
+#include "runner.h"
+#include "matrices.h"
+#include "transformations.h"
+
+static bool planes_test_0(const char ** scenario)
+{
+  *scenario = "The normal of a plane is constant everywhere";
+
+  struct shape p = plane();
+  struct tuple n1 = plane_normal_at(point(0.0f, 0.0f, 0.0f));
+  struct tuple n2 = plane_normal_at(point(10.0f, 0.0f, -10.0f));
+  struct tuple n3 = plane_normal_at(point(-5.0f, 0.0f, 150.0f));
+  return
+    tuple_equal(n1, vector(0.0f, 1.0f, 0.0f)) &&
+    tuple_equal(n2, vector(0.0f, 1.0f, 0.0f)) &&
+    tuple_equal(n3, vector(0.0f, 1.0f, 0.0f));
+}
+
+static bool planes_test_1(const char ** scenario)
+{
+  *scenario = "Intersect with a ray parallel to the plane";
+
+  struct shape p = plane();
+  struct ray r = ray(point(0.0f, 10.0f, 0.0f), vector(0.0f, 0.0f, 1.0f));
+  struct intersections xs;
+  xs.count = 0;
+  plane_intersect(&p, r, &xs);
+  return xs.count == 0;
+}
+
+static bool planes_test_2(const char ** scenario)
+{
+  *scenario = "Intersect with a coplanar ray";
+
+  struct shape p = plane();
+  struct ray r = ray(point(0.0f, 0.0f, 0.0f), vector(0.0f, 0.0f, 1.0f));
+  struct intersections xs;
+  xs.count = 0;
+  plane_intersect(&p, r, &xs);
+  return xs.count == 0;
+}
+
+static bool planes_test_3(const char ** scenario)
+{
+  *scenario = "A ray intersecting a plane from above";
+
+  struct shape p = plane();
+  struct ray r = ray(point(0.0f, 1.0f, 0.0f), vector(0.0f, -1.0f, 0.0f));
+  struct intersections xs;
+  xs.count = 0;
+  plane_intersect(&p, r, &xs);
+  return
+    xs.count == 1 &&
+    float_equal(xs.i[0].t, 1.0f) &&
+    xs.i[0].object == &p;
+}
+
+static bool planes_test_4(const char ** scenario)
+{
+  *scenario = "A ray intersecting a plane from below";
+
+  struct shape p = plane();
+  struct ray r = ray(point(0.0f, -1.0f, 0.0f), vector(0.0f, 1.0f, 1.0f));
+  struct intersections xs;
+  xs.count = 0;
+  plane_intersect(&p, r, &xs);
+  return
+    xs.count == 1 &&
+    float_equal(xs.i[0].t, 1.0f) &&
+    xs.i[0].object == &p;
+}
+
+test_t planes_tests[] = {
+  planes_test_0,
+  planes_test_1,
+  planes_test_2,
+  planes_test_3,
+  planes_test_4,
+};
+
+RUNNER(planes_tests);
diff --git a/test/test_shapes.c b/test/test_shapes.c
new file mode 100644
index 0000000..63cb6e9
--- /dev/null
+++ b/test/test_shapes.c
@@ -0,0 +1,121 @@
+#include <stdbool.h>
+#include <stdio.h>
+
+#include "shapes.h"
+#include "intersections_shapes.h"
+#include "transformations.h"
+#include "runner.h"
+#include "rays.h"
+#include "spheres.h"
+
+static bool shapes_test_0(const char ** scenario)
+{
+  *scenario = "A shape's default transformation";
+
+  struct shape s = shape();
+  struct mat4x4 identity = mat4x4_identity();
+
+  return mat4x4_equal(&s.transform, &identity);
+}
+
+static bool shapes_test_1(const char ** scenario)
+{
+  *scenario = "Changing a shape's transformation";
+
+  struct shape s = shape();
+  struct mat4x4 t = translation(2.0f, 3.0f, 4.0f);
+  s.transform = t;
+
+  return mat4x4_equal(&s.transform, &t);
+}
+
+static bool shapes_test_2(const char ** scenario)
+{
+  *scenario = "A shape has a default material";
+
+  struct shape s = shape();
+  struct material m = s.material;
+  return material_equal(m, material());
+}
+
+static bool shapes_test_3(const char ** scenario)
+{
+  *scenario = "A shape may be assigned a material";
+
+  struct shape s = shape();
+  struct material m = material();
+  m.ambient = 1.0f;
+  s.material = m;
+  return material_equal(s.material, m);
+}
+
+static bool shapes_test_4(const char ** scenario)
+{
+  *scenario = "Intersecting a scaled shape with a ray";
+
+  struct ray r = ray(point(0.0f, 0.0f, -5.0f), vector(0.0f, 0.0f, 1.0f));
+  struct shape s = shape();
+  s.transform = scaling(2.0f, 2.0f, 2.0f);
+  struct intersections xs;
+  xs.count = 0;
+  intersect(&s, r, &xs);
+
+  return
+    tuple_equal(intersections_saved_ray.origin, point(0.0f, 0.0f, -2.5f)) &&
+    tuple_equal(intersections_saved_ray.direction, vector(0.0f, 0.0f, 0.5f));
+}
+
+static bool shapes_test_5(const char ** scenario)
+{
+  *scenario = "Intersecting a translated shape with a ray";
+
+  struct ray r = ray(point(0.0f, 0.0f, -5.0f), vector(0.0f, 0.0f, 1.0f));
+  struct shape s = shape();
+  s.transform = translation(5.0f, 0.0f, 0.0f);
+  struct intersections xs;
+  xs.count = 0;
+  intersect(&s, r, &xs);
+
+  return
+    tuple_equal(intersections_saved_ray.origin, point(-5.0f, 0.0f, -5.0f)) &&
+    tuple_equal(intersections_saved_ray.direction, vector(0.0f, 0.0f, 1.0f));
+}
+
+static bool shapes_test_6(const char ** scenario)
+{
+  *scenario = "Computing the normal on a translated shape";
+
+  struct shape s = shape();
+  s.transform = translation(0.0f, 1.0f, 0.0f);
+
+  struct tuple n = normal_at(&s, point(0.0f, 1.70711f, -0.70711));
+
+  return tuple_equal(n, vector(0.0f, 0.70711f, -0.70711f));
+}
+
+static bool shapes_test_7(const char ** scenario)
+{
+  *scenario = "Computing the normal on a transformed shape";
+  struct shape s = shape();
+  struct mat4x4 scale = scaling(1.0f, 0.5f, 1.0f);
+  struct mat4x4 rotate = rotation_z(pi / 5.0f);
+  struct mat4x4 m = mat4x4_mul_m(&scale, &rotate);
+  s.transform = m;
+
+  struct tuple n = normal_at(&s, point(0.0f, 0.7071067811865476, -0.7071067811865476));
+
+  return tuple_equal(n, vector(0.0f, 0.97014f, -0.24254f));
+}
+
+test_t shape_tests[] = {
+  shapes_test_0,
+  shapes_test_1,
+  shapes_test_2,
+  shapes_test_3,
+  shapes_test_4,
+  shapes_test_5,
+  shapes_test_6,
+  shapes_test_7,
+};
+
+RUNNER(shape_tests)
diff --git a/test/test_spheres.c b/test/test_spheres.c
index 0a0afb5..c2849a3 100644
--- a/test/test_spheres.c
+++ b/test/test_spheres.c
@@ -3,7 +3,7 @@
 
 #include "rays.h"
 #include "spheres.h"
-#include "intersections.h"
+#include "intersections_shapes.h"
 #include "runner.h"
 #include "matrices.h"
 #include "transformations.h"
@@ -13,7 +13,7 @@ static bool spheres_test_0(const char ** scenario)
   *scenario = "A ray intersects a sphere at two points";
 
   struct ray r = ray(point(0.0f, 0.0f, -5.0f), vector(0.0f, 0.0f, 1.0f));
-  struct sphere s = sphere();
+  struct shape s = sphere();
   struct intersections xs;
   xs.count = 0;
   intersect(&s, r, &xs);
@@ -29,7 +29,7 @@ static bool spheres_test_1(const char ** scenario)
   *scenario = "A ray intersects a sphere at a tangent";
 
   struct ray r = ray(point(0.0f, 1.0f, -5.0f), vector(0.0f, 0.0f, 1.0f));
-  struct sphere s = sphere();
+  struct shape s = sphere();
   struct intersections xs;
   xs.count = 0;
   intersect(&s, r, &xs);
@@ -45,7 +45,7 @@ static bool spheres_test_2(const char ** scenario)
   *scenario = "A ray misses a sphere";
 
   struct ray r = ray(point(0.0f, 2.0f, -5.0f), vector(0.0f, 0.0f, 1.0f));
-  struct sphere s = sphere();
+  struct shape s = sphere();
   struct intersections xs;
   xs.count = 0;
   intersect(&s, r, &xs);
@@ -58,7 +58,7 @@ static bool spheres_test_3(const char ** scenario)
   *scenario = "A ray originates in a sphere";
 
   struct ray r = ray(point(0.0f, 0.0f, 0.0f), vector(0.0f, 0.0f, 1.0f));
-  struct sphere s = sphere();
+  struct shape s = sphere();
   struct intersections xs;
   xs.count = 0;
   intersect(&s, r, &xs);
@@ -74,7 +74,7 @@ static bool spheres_test_4(const char ** scenario)
   *scenario = "A sphere is behind a ray";
 
   struct ray r = ray(point(0.0f, 0.0f, 5.0f), vector(0.0f, 0.0f, 1.0f));
-  struct sphere s = sphere();
+  struct shape s = sphere();
   struct intersections xs;
   xs.count = 0;
   intersect(&s, r, &xs);
@@ -90,7 +90,7 @@ static bool spheres_test_5(const char ** scenario)
   *scenario = "Intersect sets the object on the intersection";
 
   struct ray r = ray(point(0.0f, 0.0f, -5.0f), vector(0.0f, 0.0f, 1.0f));
-  struct sphere s = sphere();
+  struct shape s = sphere();
   struct intersections xs;
   xs.count = 0;
   intersect(&s, r, &xs);
@@ -102,32 +102,11 @@ static bool spheres_test_5(const char ** scenario)
 }
 
 static bool spheres_test_6(const char ** scenario)
-{
-  *scenario = "A sphere's default transformation";
-
-  struct sphere s = sphere();
-  struct mat4x4 identity = mat4x4_identity();
-
-  return mat4x4_equal(&s.transform, &identity);
-}
-
-static bool spheres_test_7(const char ** scenario)
-{
-  *scenario = "Changing a sphere's transformation";
-
-  struct sphere s = sphere();
-  struct mat4x4 t = translation(2.0f, 3.0f, 4.0f);
-  s.transform = t;
-
-  return mat4x4_equal(&s.transform, &t);
-}
-
-static bool spheres_test_8(const char ** scenario)
 {
   *scenario = "Intersecting a scaled sphere with a ray";
 
   struct ray r = ray(point(0.0f, 0.0f, -5.0f), vector(0.0f, 0.0f, 1.0f));
-  struct sphere s = sphere();
+  struct shape s = sphere();
   s.transform = scaling(2.0f, 2.0f, 2.0f);
   struct intersections xs;
   xs.count = 0;
@@ -139,12 +118,12 @@ static bool spheres_test_8(const char ** scenario)
     float_equal(xs.i[1].t, 7.0f);
 }
 
-static bool spheres_test_9(const char ** scenario)
+static bool spheres_test_7(const char ** scenario)
 {
   *scenario = "Intersecting a translated sphere with a ray";
 
   struct ray r = ray(point(0.0f, 0.0f, 5.0f), vector(0.0f, 0.0f, 1.0f));
-  struct sphere s = sphere();
+  struct shape s = sphere();
   s.transform = translation(5.0f, 0.0f, 0.0f);
   struct intersections xs;
   xs.count = 0;
@@ -153,103 +132,83 @@ static bool spheres_test_9(const char ** scenario)
   return xs.count == 0;
 }
 
-static bool spheres_test_10(const char ** scenario)
+static bool spheres_test_8(const char ** scenario)
 {
   *scenario = "The normal on a sphere at a point on the x axis";
 
-  struct sphere s = sphere();
-  struct tuple n = sphere_normal_at(&s, point(1.0f, 0.0f, 0.0f));
+  struct shape s = sphere();
+  struct tuple n = normal_at(&s, point(1.0f, 0.0f, 0.0f));
   return tuple_equal(n, vector(1.0f, 0.0f, 0.0f));
 }
 
+static bool spheres_test_9(const char ** scenario)
+{
+  *scenario = "The normal on a sphere at a point on the y axis";
+
+  struct shape s = sphere();
+  struct tuple n = normal_at(&s, point(0.0f, 1.0f, 0.0f));
+  return tuple_equal(n, vector(0.0f, 1.0f, 0.0f));
+}
+
+static bool spheres_test_10(const char ** scenario)
+{
+  *scenario = "The normal on a sphere at a point on the z axis";
+
+  struct shape s = sphere();
+  struct tuple n = normal_at(&s, point(0.0f, 0.0f, 1.0f));
+  return tuple_equal(n, vector(0.0f, 0.0f, 1.0f));
+}
+
 static bool spheres_test_11(const char ** scenario)
-{
-  *scenario = "The normal on a sphere at a point on the y axis";
-
-  struct sphere s = sphere();
-  struct tuple n = sphere_normal_at(&s, point(0.0f, 1.0f, 0.0f));
-  return tuple_equal(n, vector(0.0f, 1.0f, 0.0f));
-}
-
-static bool spheres_test_12(const char ** scenario)
-{
-  *scenario = "The normal on a sphere at a point on the z axis";
-
-  struct sphere s = sphere();
-  struct tuple n = sphere_normal_at(&s, point(0.0f, 0.0f, 1.0f));
-  return tuple_equal(n, vector(0.0f, 0.0f, 1.0f));
-}
-
-static bool spheres_test_13(const char ** scenario)
 {
   *scenario = "The normal on a sphere at a nonaxial point";
 
-  struct sphere s = sphere();
-  struct tuple n = sphere_normal_at(&s, point(0.5773502691896257,
-                                              0.5773502691896257,
-                                              0.5773502691896257));
+  struct shape s = sphere();
+  struct tuple n = normal_at(&s, point(0.5773502691896257,
+                                       0.5773502691896257,
+                                       0.5773502691896257));
   return tuple_equal(n, vector(0.5773502691896257,
                                0.5773502691896257,
                                0.5773502691896257));
 }
 
-static bool spheres_test_14(const char ** scenario)
+static bool spheres_test_12(const char ** scenario)
 {
   *scenario = "The normal is a normalized vector";
 
-  struct sphere s = sphere();
-  struct tuple n = sphere_normal_at(&s, point(0.5773502691896257,
-                                              0.5773502691896257,
-                                              0.5773502691896257));
+  struct shape s = sphere();
+  struct tuple n = normal_at(&s, point(0.5773502691896257,
+                                       0.5773502691896257,
+                                       0.5773502691896257));
   return tuple_equal(n, tuple_normalize(n));
 }
 
-static bool spheres_test_15(const char ** scenario)
+static bool spheres_test_13(const char ** scenario)
 {
   *scenario = "Computing the normal on a translated sphere";
 
-  struct sphere s = sphere();
+  struct shape s = sphere();
   s.transform = translation(0.0f, 1.0f, 0.0f);
-  struct tuple n = sphere_normal_at(&s, point(0.0f, 1.70711f, -0.70711));
+  struct tuple n = normal_at(&s, point(0.0f, 1.70711f, -0.70711));
 
   return tuple_equal(n, vector(0.0f, 0.70711f, -0.70711f));
 }
 
-static bool spheres_test_16(const char ** scenario)
+static bool spheres_test_14(const char ** scenario)
 {
   *scenario = "Computing the normal on a transformed sphere";
 
-  struct sphere s = sphere();
+  struct shape s = sphere();
   struct mat4x4 scale = scaling(1.0f, 0.5f, 1.0f);
   struct mat4x4 rotate = rotation_z(pi / 5.0f);
   struct mat4x4 m = mat4x4_mul_m(&scale, &rotate);
   s.transform = m;
 
-  struct tuple n = sphere_normal_at(&s, point(0.0f, 0.7071067811865476, -0.7071067811865476));
+  struct tuple n = normal_at(&s, point(0.0f, 0.7071067811865476, -0.7071067811865476));
 
   return tuple_equal(n, vector(0.0f, 0.97014f, -0.24254f));
 }
 
-static bool spheres_test_17(const char ** scenario)
-{
-  *scenario = "A sphere has a default material";
-
-  struct sphere s = sphere();
-  struct material m = s.material;
-  return material_equal(m, material());
-}
-
-static bool spheres_test_18(const char ** scenario)
-{
-  *scenario = "A sphere may be assigned a material";
-
-  struct sphere s = sphere();
-  struct material m = material();
-  m.ambient = 1.0f;
-  s.material = m;
-  return material_equal(s.material, m);
-}
-
 test_t spheres_tests[] = {
   spheres_test_0,
   spheres_test_1,
@@ -266,10 +225,6 @@ test_t spheres_tests[] = {
   spheres_test_12,
   spheres_test_13,
   spheres_test_14,
-  spheres_test_15,
-  spheres_test_16,
-  spheres_test_17,
-  spheres_test_18,
 };
 
 RUNNER(spheres_tests);
diff --git a/test/test_world.c b/test/test_world.c
index c099367..126c822 100644
--- a/test/test_world.c
+++ b/test/test_world.c
@@ -20,11 +20,11 @@ static bool world_test_1(const char ** scenario)
   *scenario = "The default world";
 
   struct light light = point_light(point(-10.0f, 10.0f, -10.0f), color(1.0f, 1.0f, 1.0f));
-  struct sphere s1 = sphere();
+  struct shape s1 = sphere();
   s1.material.color = color(0.8f, 1.0f, 0.6f);
   s1.material.diffuse = 0.7f;
   s1.material.specular = 0.2f;
-  struct sphere s2 = sphere();
+  struct shape s2 = sphere();
   s2.transform = scaling(0.5f, 0.5f, 0.5f);
   struct world w = world_default();
   return
@@ -61,7 +61,7 @@ static bool world_test_3(const char ** scenario)
 
   struct world w = world_default();
   struct ray r = ray(point(0.0f, 0.0f, -5.0f), vector(0.0f, 0.0f, 1.0f));
-  struct sphere * shape = &w.objects[0];
+  struct shape * shape = &w.objects[0];
   struct intersection i = intersection(4.0f, shape);
   struct computations comps = prepare_computations(i, r);
   struct tuple c = world_shade_hit(&w, &comps);
@@ -76,7 +76,7 @@ static bool world_test_4(const char ** scenario)
   struct world w = world_default();
   w.light = point_light(point(0.0f, 0.25f, 0.0f), color(1.0f, 1.0f, 1.0f));
   struct ray r = ray(point(0.0f, 0.0f, 0.0f), vector(0.0f, 0.0f, 1.0f));
-  struct sphere * shape = &w.objects[1];
+  struct shape * shape = &w.objects[1];
   struct intersection i = intersection(0.5f, shape);
   struct computations comps = prepare_computations(i, r);
   struct tuple c = world_shade_hit(&w, &comps);
@@ -111,9 +111,9 @@ static bool world_test_7(const char ** scenario)
   *scenario = "The color with an intersection behind the ray";
 
   struct world w = world_default();
-  struct sphere * outer = &w.objects[0];
+  struct shape * outer = &w.objects[0];
   outer->material.ambient = 1.0f;
-  struct sphere * inner = &w.objects[1];
+  struct shape * inner = &w.objects[1];
   inner->material.ambient = 1.0f;
   struct ray r = ray(point(0.0f, 0.0f, 0.75f), vector(0.0f, 0.0f, -1.0f));
   struct tuple c = world_color_at(&w, r);
@@ -167,9 +167,9 @@ static bool world_test_12(const char ** scenario)
 
   struct world w = world();
   w.light = point_light(point(0.0f, 0.0f, -10.0f), color(1.0f, 1.0f, 1.0f));
-  struct sphere s1 = sphere();
+  struct shape s1 = sphere();
   w.objects[0] = s1;
-  struct sphere s2 = sphere();
+  struct shape s2 = sphere();
   s2.transform = translation(0.0f, 0.0f, 10.0f);
   w.objects[1] = s2;
   w.object_count = 2;
diff --git a/world.h b/world.h
index 700ffe9..39922fe 100644
--- a/world.h
+++ b/world.h
@@ -3,7 +3,7 @@
 #include "lights.h"
 #include "spheres.h"
 #include "transformations.h"
-#include "intersections.h"
+#include "intersections_shapes.h"
 #include "rays.h"
 #include "materials.h"
 
@@ -12,7 +12,7 @@
 struct world {
   struct light light;
   int object_count;
-  struct sphere objects[WORLD_MAX_OBJECTS];
+  struct shape objects[WORLD_MAX_OBJECTS];
 };
 
 inline static struct world world()
@@ -25,11 +25,11 @@ inline static struct world world()
 
 inline static struct world world_default()
 {
-  struct sphere s1 = sphere();
+  struct shape s1 = sphere();
   s1.material.color = color(0.8f, 1.0f, 0.6f);
   s1.material.diffuse = 0.7f;
   s1.material.specular = 0.2f;
-  struct sphere s2 = sphere();
+  struct shape s2 = sphere();
   s2.transform = scaling(0.5f, 0.5f, 0.5f);
 
   return (struct world){