diff --git a/src/assembly.rs b/src/assembly.rs
index 1a449ef..62efe32 100644
--- a/src/assembly.rs
+++ b/src/assembly.rs
@@ -9,19 +9,19 @@ use ray::Ray;
 #[derive(Debug)]
 pub struct Assembly {
     // Instance list
-    instances: Vec<Instance>,
-    xforms: Vec<Matrix4x4>,
+    pub instances: Vec<Instance>,
+    pub xforms: Vec<Matrix4x4>,
 
     // Object list
-    objects: Vec<Object>,
+    pub objects: Vec<Object>,
     object_map: HashMap<String, usize>, // map Name -> Index
 
     // Assembly list
-    assemblies: Vec<Assembly>,
+    pub assemblies: Vec<Assembly>,
     assembly_map: HashMap<String, usize>, // map Name -> Index
 
     // Object accel
-    object_accel: BVH,
+    pub object_accel: BVH,
 }
 
 impl Assembly {
@@ -37,17 +37,6 @@ impl Assembly {
         }
     }
 
-    // TODO: this is just temporary.  Remove this and move tracing functionality
-    // into the tracer.
-    pub fn intersect_rays(&self, rays: &mut [Ray], isects: &mut [SurfaceIntersection]) {
-        for obj in self.objects.iter() {
-            match obj {
-                &Object::Surface(ref surface) => {
-                    surface.intersect_rays(rays, isects);
-                }
-            }
-        }
-    }
 
 
     pub fn add_object(&mut self, name: &str, obj: Object) {
@@ -64,7 +53,7 @@ pub enum Object {
 
 
 #[derive(Debug, Copy, Clone)]
-enum Instance {
+pub enum Instance {
     Object {
         data_index: usize,
         transform_indices: (usize, usize),
diff --git a/src/renderer.rs b/src/renderer.rs
index 27435d0..3dd37f9 100644
--- a/src/renderer.rs
+++ b/src/renderer.rs
@@ -2,6 +2,7 @@
 
 use std::path::Path;
 
+use tracer::Tracer;
 use camera::Camera;
 use halton;
 use math::fast_logit;
@@ -21,7 +22,7 @@ pub struct Renderer {
 impl Renderer {
     pub fn render(&self) {
         let mut rays = Vec::new();
-        let mut isects = Vec::new();
+        let mut tracer = Tracer::from_assembly(&self.scene.root);
         let mut img = Image::new(self.resolution.0, self.resolution.1);
 
         // Render image of ray-traced triangle
@@ -34,7 +35,6 @@ impl Renderer {
 
                 // Generate rays
                 rays.clear();
-                isects.clear();
                 for si in 0..self.spp {
                     let mut ray = {
                         let filter_x = fast_logit(halton::sample(3, offset + si as u32), 1.5);
@@ -47,11 +47,10 @@ impl Renderer {
                     };
                     ray.id = si as u32;
                     rays.push(ray);
-                    isects.push(surface::SurfaceIntersection::Miss);
                 }
 
                 // Test rays against scene
-                self.scene.root.intersect_rays(&mut rays, &mut isects);
+                let isects = tracer.trace(&rays);
 
                 // Calculate color based on ray hits
                 let mut r = 0.0;
diff --git a/src/surface/mod.rs b/src/surface/mod.rs
index f38e5e7..bb0abdc 100644
--- a/src/surface/mod.rs
+++ b/src/surface/mod.rs
@@ -8,7 +8,7 @@ use ray::Ray;
 use math::{Point, Normal, Matrix4x4};
 
 
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub enum SurfaceIntersection {
     Miss,
     Occlude,
diff --git a/src/tracer.rs b/src/tracer.rs
index 7c5252b..956b5fd 100644
--- a/src/tracer.rs
+++ b/src/tracer.rs
@@ -1,10 +1,63 @@
+use std::iter;
+use std::slice;
+
 use math::Matrix4x4;
+use assembly::{Assembly, Object};
 use ray::Ray;
 use surface::SurfaceIntersection;
 
 pub struct Tracer<'a> {
+    root: &'a Assembly,
+    rays: Vec<Ray>, // Should only be used from trace(), not any other methods
     xform_stack: Vec<Matrix4x4>,
-    world_rays: &'a [Ray],
-    intersections: &'a mut [SurfaceIntersection],
-    rays: Vec<Ray>,
+    isects: Vec<SurfaceIntersection>,
+}
+
+impl<'a> Tracer<'a> {
+    pub fn from_assembly(assembly: &'a Assembly) -> Tracer<'a> {
+        Tracer {
+            root: assembly,
+            xform_stack: Vec::new(),
+            rays: Vec::new(),
+            isects: Vec::new(),
+        }
+    }
+
+    pub fn trace<'b>(&'b mut self, wrays: &[Ray]) -> &'b [SurfaceIntersection] {
+        // Ready the rays
+        self.rays.clear();
+        self.rays.reserve(wrays.len());
+        self.rays.extend(wrays.iter());
+
+        // Ready the isects
+        self.isects.clear();
+        self.isects.reserve(wrays.len());
+        self.isects.extend(iter::repeat(SurfaceIntersection::Miss).take(wrays.len()));
+
+        // Start tracing
+        let ray_refs = unsafe {
+            // IMPORTANT NOTE:
+            // We're creating an unsafe non-lifetime-bound slice of self.rays
+            // here so that we can pass it to trace_assembly() without
+            // conflicting with self.
+            // Because of this, it is absolutely CRITICAL that self.rays
+            // NOT be used in any other methods.  The rays should only be
+            // accessed in other methods via the mutable slice passed directly
+            // to them in their function parameters.
+            slice::from_raw_parts_mut(self.rays.as_mut_ptr(), self.rays.len())
+        };
+        self.trace_assembly(self.root, wrays, ray_refs);
+
+        return &self.isects;
+    }
+
+    fn trace_assembly<'b>(&'b mut self, assembly: &Assembly, wrays: &[Ray], rays: &mut [Ray]) {
+        for obj in assembly.objects.iter() {
+            match obj {
+                &Object::Surface(ref surface) => {
+                    surface.intersect_rays(rays, &mut self.isects);
+                }
+            }
+        }
+    }
 }
diff --git a/todo.txt b/todo.txt
index edd8cbc..3d9653a 100644
--- a/todo.txt
+++ b/todo.txt
@@ -1 +1,4 @@
-- Implement a basic camera.
\ No newline at end of file
+- Implement a Tracer to handle ray tracing responsibilities, with hierarchical
+  instancing, etc.
+- Basic scene parsing with triangle meshes.
+- Unit tests for scene parsing.
\ No newline at end of file