diff --git a/src/test/test_vec.rs b/src/test/test_vec.rs
index eed05ba..e13245b 100644
--- a/src/test/test_vec.rs
+++ b/src/test/test_vec.rs
@@ -81,6 +81,8 @@ fn test_Vec2_geometric() {
     let b0 = Vec2::new(3f, 4f); // (3, 4, 5) Pythagorean triple
     let b = a.add_v(&b0);
     
+    // TODO: test normalize and normalize_self
+    
     assert a.length() == 13f;
     assert a.length2() == 13f * 13f;
     
@@ -94,6 +96,10 @@ fn test_Vec2_geometric() {
     let d = Vec2::new( 1.0f,  0.0f);
     
     assert c.lerp(&d, 0.75f) == Vec2::new(0.250f, -0.250f);
+    
+    let mut mut_c = c;
+    mut_c.lerp_self(&d, &0.75f);
+    assert mut_c == c.lerp(&d, 0.75f);
 }
 
 #[test]
@@ -189,6 +195,8 @@ fn test_Vec3_geometric() {
     let b0 = Vec3::new(1f, 4f, 8f); // (1, 4, 8, 9) Pythagorean quadruple
     let b = a.add_v(&b0);
     
+    // TODO: test normalize and normalize_self
+    
     assert a.length() == 7f;
     assert a.length2() == 7f * 7f;
     
@@ -202,6 +210,10 @@ fn test_Vec3_geometric() {
     let d = Vec3::new( 1.0f,  0.0f, 0.5f);
     
     assert c.lerp(&d, 0.75f) == Vec3::new(0.250f, -0.250f, 0.625f);
+    
+    let mut mut_c = c;
+    mut_c.lerp_self(&d, &0.75f);
+    assert mut_c == c.lerp(&d, 0.75f);
 }
 
 #[test]
@@ -297,6 +309,8 @@ fn test_Vec4_geometric() {
     let b0 = Vec4::new(1f, 2f, 8f, 10f); // (1, 2, 8, 10, 13) Pythagorean quintuple
     let b = a.add_v(&b0);
     
+    // TODO: test normalize and normalize_self
+    
     assert a.length() == 11f;
     assert a.length2() == 11f * 11f;
     
@@ -310,4 +324,8 @@ fn test_Vec4_geometric() {
     let d = Vec4::new( 1.0f,  0.0f, 0.5f, 1.0f);
     
     assert c.lerp(&d, 0.75f) == Vec4::new(0.250f, -0.250f, 0.625f, 1.250f);
+    
+    let mut mut_c = c;
+    mut_c.lerp_self(&d, &0.75f);
+    assert mut_c == c.lerp(&d, 0.75f);
 }
\ No newline at end of file
diff --git a/src/vec.rs b/src/vec.rs
index 487cd3d..1fc005e 100644
--- a/src/vec.rs
+++ b/src/vec.rs
@@ -77,7 +77,7 @@ pub trait NumericVector<T>: Vector<T>, Neg<self> {
     pure fn div_t(&self, value: T) -> self;
     
     /**
-     * Returns the sum of the vector with `other`
+     * Returns the sum of the vector and `other`
      */
     pure fn add_v(&self, other: &self) -> self;
     
@@ -112,12 +112,12 @@ pub trait MutableNumericVector<T>: MutableVector<&self/T>, NumericVector<T> {
     fn div_self_t(&mut self, value: T);
     
     /**
-     * Add a vector
+     * Set to the sum of the vector and `other`
      */
     fn add_self_v(&mut self, other: &self);
     
     /**
-     * Subtract a vector
+     * Set to the difference between the vector and `other`
      */
     fn sub_self_v(&mut self, other: &self);
 }
@@ -137,6 +137,7 @@ pub trait NumericVector3<T>: NumericVector<T> {
     // static pure fn unit_x() -> self;
     // static pure fn unit_y() -> self;
     // static pure fn unit_z() -> self;
+    
     /**
      * Returns the cross product of the vector and `other`
      */
@@ -198,6 +199,19 @@ pub trait GeometricVector<T>: NumericVector<T> {
     pure fn lerp(&self, other: &self, amount: T) -> self;
 }
 
+pub trait MutableGeometricVector<T>: MutableNumericVector<&self/T>,
+                                     GeometricVector<T> {
+    /**
+     * Normalize the vector
+     */
+    fn normalize_self(&mut self);
+    
+    /**
+     * Linearly intoperlate the vector towards `other`
+     */
+    fn lerp_self(&mut self, other: &self, amount: T);
+}
+
 
 
 
@@ -381,6 +395,19 @@ pub impl<T:Copy Number Exp> Vec2<T>: GeometricVector<T> {
     }
 }
 
+pub impl<T:Copy Number Exp> Vec2<T>: MutableGeometricVector<&self/T> {
+    #[inline(always)]
+    fn normalize_self(&mut self) {
+        let mut n: T = Number::from(1); 
+        n /= self.length();
+        self.mul_self_t(&n);
+    }
+    
+    fn lerp_self(&mut self, other: &Vec2<T>, amount: &T) {
+        self.add_self_v(&other.sub_v(&*self).mul_t(*amount));
+    }
+}
+
 pub impl<T:Copy DefaultEq> Vec2<T>: Eq {
     #[inline(always)]
     pure fn eq(&self, other: &Vec2<T>) -> bool {
@@ -622,6 +649,19 @@ pub impl<T:Copy Number Exp> Vec3<T>: GeometricVector<T> {
     }
 }
 
+pub impl<T:Copy Number Exp> Vec3<T>: MutableGeometricVector<&self/T> {
+    #[inline(always)]
+    fn normalize_self(&mut self) {
+        let mut n: T = Number::from(1); 
+        n /= self.length();
+        self.mul_self_t(&n);
+    }
+    
+    fn lerp_self(&mut self, other: &Vec3<T>, amount: &T) {
+        self.add_self_v(&other.sub_v(&*self).mul_t(*amount));
+    }
+}
+
 pub impl<T:Copy DefaultEq> Vec3<T>: Eq {
     #[inline(always)]
     pure fn eq(&self, other: &Vec3<T>) -> bool {
@@ -862,6 +902,19 @@ pub impl<T:Copy Number Exp> Vec4<T>: GeometricVector<T> {
     }
 }
 
+pub impl<T:Copy Number Exp> Vec4<T>: MutableGeometricVector<&self/T> {
+    #[inline(always)]
+    fn normalize_self(&mut self) {
+        let mut n: T = Number::from(1); 
+        n /= self.length();
+        self.mul_self_t(&n);
+    }
+    
+    fn lerp_self(&mut self, other: &Vec4<T>, amount: &T) {
+        self.add_self_v(&other.sub_v(&*self).mul_t(*amount));
+    }
+}
+
 pub impl<T:Copy DefaultEq> Vec4<T>: Eq {
     #[inline(always)]
     pure fn eq(&self, other: &Vec4<T>) -> bool {