diff --git a/rtiow/src/lib.rs b/rtiow/src/lib.rs
index 31e1bb2..9b789be 100644
--- a/rtiow/src/lib.rs
+++ b/rtiow/src/lib.rs
@@ -1,7 +1 @@
-#[cfg(test)]
-mod tests {
-    #[test]
-    fn it_works() {
-        assert_eq!(2 + 2, 4);
-    }
-}
+pub mod vec3;
diff --git a/rtiow/src/vec3.rs b/rtiow/src/vec3.rs
new file mode 100644
index 0000000..7ac2f07
--- /dev/null
+++ b/rtiow/src/vec3.rs
@@ -0,0 +1,217 @@
+use std::f32::consts::PI;
+use std::fmt;
+use std::num::ParseFloatError;
+use std::ops::Add;
+use std::ops::Div;
+use std::ops::Index;
+use std::ops::Mul;
+use std::ops::Sub;
+use std::str;
+
+#[derive(Default, Debug, PartialEq, Copy, Clone)]
+pub struct Vec3 {
+    x: f32,
+    y: f32,
+    z: f32,
+}
+
+fn cross(v1: Vec3, v2: Vec3) -> Vec3 {
+    Vec3 {
+        x: v1.y * v2.z - v1.z * v2.y,
+        y: v1.x * v2.z - v1.z * v2.x,
+        z: v1.x * v2.y - v1.y * v2.x,
+    }
+}
+
+fn dot(v1: Vec3, v2: Vec3) -> f32 {
+    v1.x * v2.x + v1.y * v2.y + v1.z * v2.z
+}
+
+impl Vec3 {
+    pub fn new(x: f32, y: f32, z: f32) -> Vec3 {
+        Vec3 { x, y, z }
+    }
+
+    pub fn length(self) -> f32 {
+        self.squared_length().sqrt()
+    }
+
+    pub fn squared_length(self) -> f32 {
+        self.x * self.x + self.y * self.y + self.z * self.z
+    }
+
+    pub fn unit_vector(self) -> Vec3 {
+        let k = 1. / self.length();
+        Vec3 {
+            x: self.x / k,
+            y: self.y / k,
+            z: self.z / k,
+        }
+    }
+
+    pub fn make_unit_vector(&mut self) {
+        *self = self.unit_vector();
+    }
+}
+
+impl fmt::Display for Vec3 {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{} {} {}", self.x, self.y, self.z)
+    }
+}
+
+impl str::FromStr for Vec3 {
+    type Err = ParseFloatError;
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let coords: Vec<&str> = s.split(" ").collect();
+        Ok(Vec3 {
+            x: coords[0].parse::<f32>()?,
+            y: coords[1].parse::<f32>()?,
+            z: coords[2].parse::<f32>()?,
+        })
+    }
+}
+
+impl Add for Vec3 {
+    type Output = Vec3;
+
+    fn add(self, r: Vec3) -> Vec3 {
+        Vec3 {
+            x: self.x + r.x,
+            y: self.y + r.y,
+            z: self.z + r.z,
+        }
+    }
+}
+
+impl Div<f32> for Vec3 {
+    type Output = Vec3;
+
+    fn div(self, r: f32) -> Vec3 {
+        Vec3 {
+            x: self.x / r,
+            y: self.y / r,
+            z: self.z / r,
+        }
+    }
+}
+
+impl Index<usize> for Vec3 {
+    type Output = f32;
+    fn index(&self, idx: usize) -> &f32 {
+        match idx {
+            0 => &self.x,
+            1 => &self.y,
+            2 => &self.z,
+            _ => panic!(format!("idx {} out of range for vec3", idx)),
+        }
+    }
+}
+
+impl Mul for Vec3 {
+    type Output = Vec3;
+
+    fn mul(self, r: Vec3) -> Vec3 {
+        Vec3 {
+            x: self.x * r.x,
+            y: self.y * r.y,
+            z: self.z * r.z,
+        }
+    }
+}
+
+impl Mul<f32> for Vec3 {
+    type Output = Vec3;
+
+    fn mul(self, r: f32) -> Vec3 {
+        Vec3 {
+            x: self.x * r,
+            y: self.y * r,
+            z: self.z * r,
+        }
+    }
+}
+
+impl Sub for Vec3 {
+    type Output = Vec3;
+
+    fn sub(self, r: Vec3) -> Vec3 {
+        Vec3 {
+            x: self.x - r.x,
+            y: self.y - r.y,
+            z: self.z - r.z,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::str::FromStr;
+
+    use super::*;
+
+    #[test]
+    fn vec_add() {
+        let v0 = Vec3::new(1., 2., 3.);
+        let v1 = Vec3::new(1., 1., 1.);
+        assert_eq!(v0 + v1, Vec3::new(2., 3., 4.));
+    }
+
+    #[test]
+    fn vec_div() {
+        let v0 = Vec3::new(1., 2., 4.);
+        assert_eq!(v0 / 2., Vec3::new(0.5, 1., 2.));
+    }
+
+    #[test]
+    fn vec_mul() {
+        let v0 = Vec3::new(1., 2., 4.);
+        assert_eq!(v0 * 0.5, Vec3::new(0.5, 1., 2.));
+        assert_eq!(v0 * v0, Vec3::new(1., 4., 16.));
+    }
+
+    #[test]
+    fn vec_sub() {
+        let v0 = Vec3::new(1., 2., 3.);
+        let v1 = Vec3::new(1., 1., 1.);
+        assert_eq!(v0 - v1, Vec3::new(0., 1., 2.));
+    }
+
+    #[test]
+    fn vec_idx() {
+        let v0 = Vec3::new(1., 2., 3.);
+        assert_eq!(v0[2], 3.);
+    }
+
+    #[test]
+    fn vec_display() {
+        let v0 = Vec3::new(1., 2., 3.);
+        assert_eq!(format!("{}", v0), "1 2 3".to_owned());
+    }
+
+    #[test]
+    fn vec_from_str() {
+        assert_eq!(Vec3::from_str("1. 2. 3.").unwrap(), Vec3::new(1., 2., 3.));
+    }
+
+    #[test]
+    fn vec_str_roundtrip() {
+        let v = Vec3::from_str("1 2 3").unwrap();
+        let s = format!("{}", v);
+        assert_eq!(v, Vec3::from_str(&s).unwrap());
+    }
+
+    #[test]
+    fn vec_dot() {
+        let v0 = Vec3::new(1., 0., 0.);
+        let v1 = Vec3::new(-1., 0., 0.);
+        assert_eq!(dot(v0, v1), v0.length() * v1.length() * PI.cos());
+    }
+
+    #[test]
+    fn vec_cross() {
+        let v0 = Vec3::new(1., 0., 0.);
+        let v1 = Vec3::new(0., 1., 0.);
+        assert_eq!(cross(v0, v1), Vec3::new(0., 0., 1.));
+    }
+}