diff --git a/src/lib.rs b/src/lib.rs
index 81f851a..4850fd9 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -7,6 +7,7 @@ pub mod image;
 pub mod integrators;
 pub mod materials;
 pub mod mesh;
+/// Core raycasting and geometry primitives
 pub mod raycasting;
 pub mod realtype;
 pub mod sampler;
diff --git a/src/raycasting/mod.rs b/src/raycasting/mod.rs
index 1ba9875..7c6bb91 100644
--- a/src/raycasting/mod.rs
+++ b/src/raycasting/mod.rs
@@ -20,13 +20,23 @@ pub use axis_aligned_bounding_box::BoundingBox;
 pub mod bounding_volume_hierarchy;
 pub use bounding_volume_hierarchy::BoundingVolumeHierarchy;
 
+/// A ray, consisting or a start point and direction
+///
+/// This is the basic ray struct used to define things like a line-of-sight
+/// going out from the camera of a reflection from a surface.
 #[derive(Clone, Debug)]
 pub struct Ray<T: Real> {
+    /// The start point of the ray
     pub origin: Point3<T>,
+
+    /// The direction the ray goes in.
+    ///
+    /// This vector should always be kept normalized
     pub direction: Vector3<T>,
 }
 
 impl<T: Real> Ray<T> {
+    /// Create a new ray
     pub fn new(origin: Point3<T>, direction: Vector3<T>) -> Ray<T> {
         Ray {
             origin,
@@ -34,44 +44,91 @@ impl<T: Real> Ray<T> {
         }
     }
 
+    /// Return the point on the ray that is `t` units from the start
     pub fn point_at(&self, t: T) -> Point3<T> {
         self.origin + self.direction * t
     }
 
+    /// Create a new ray by moving the original ray along it's direction by `amount`
+    ///
+    /// `amount` is normally a very small number. This function is useful for ensuring
+    /// that rounding-errors don;t cause a reflection ray doesn't intersect with the point
+    /// it's reflected from.
     pub fn bias(&self, amount: T) -> Ray<T> {
         Ray::new(self.origin + self.direction * amount, self.direction)
     }
 }
 
+/// Information about a ray-primitive intersection.
+///
+/// This struct is returned by [intersect()](Intersect::intersect) and contatins all the
+/// information needed to evaluate the rendering function for that intersection.
 #[derive(Debug)]
 pub struct IntersectionInfo<T: Real> {
+    /// The distance between the ray origin and the intersection point
     pub distance: T,
+
+    /// The intersection point
     pub location: Point3<T>,
+
+    /// The surface normal at the intersection point
     pub normal: Vector3<T>,
+
+    /// The surface tangent at the intersection point
+    ///
+    /// Which surface tangent direction returned is dependent on the [Primitive](Primitive)
+    /// but should generally be smooth over any given surface
     pub tangent: Vector3<T>,
+
+    /// Another surface tangent, perpendicular to `tangent`
+    ///
+    /// The cross product or `normal` and `tangent`
     pub cotangent: Vector3<T>,
+
+    /// The direction from the intersection point back towards the ray
+    ///
+    /// Equal to `-ray.direction`
     pub retro: Vector3<T>,
+
+    /// The [Material](crate::materials::Material) which describes the optical
+    /// properties of the intersected surface
     pub material: Arc<dyn Material<T>>,
 }
 
+/// A geometric object that has a [Material](crate::materials::Material) and can be
+/// intersected with a [Ray](Ray)
 pub trait Intersect<T: Real>: Send + Sync {
     /// Test if the ray intersects the object, and return information about the object and intersection.
     fn intersect<'a>(&'a self, ray: &Ray<T>) -> Option<IntersectionInfo<T>>;
 }
 
+/// A geometric object that can be intersected with a ray
+///
+/// This is useful for objects that don't have materials (such as [BoundingBox](BoundingBox))
+/// and as a (possibly) faster alternative to [Intersect](Intersect) when only a simple
+/// intersection test is needed.
 pub trait IntersectP<T: Real>: Send + Sync {
     /// Test if the ray intersects the object, without calculating any extra information.
     fn intersect(&self, ray: &Ray<T>) -> bool;
 }
 
+/// Any geometric object for which a [BoundingBox](BoundingBox) can be calculated
 pub trait HasBoundingBox<T: Real>: Send + Sync {
+    /// The axis-aligned bounding box of the object
+    ///
+    /// The object must fit entirely inside this box.
     fn bounding_box(&self) -> BoundingBox<T>;
 }
 
+/// Any geometric object which can have an affine transformation applied to it
+///
+/// Used for moving, rotating or scaling primitives
 pub trait Transform<T: Real>: Send + Sync {
+    /// Create a new object by applying the transformation to this object.
     fn transform(&mut self, transformation: &Affine3<T>) -> &Self;
 }
 
+/// A basic geometric primitive such as a sphere or a triangle
 pub trait Primitive<T: Real>: Intersect<T> + HasBoundingBox<T> {}
 
 #[cfg(test)]