diff --git a/src/main/java/pythagoras/d/IMatrix4.java b/src/main/java/pythagoras/d/IMatrix4.java
index e284858..34b7f73 100644
--- a/src/main/java/pythagoras/d/IMatrix4.java
+++ b/src/main/java/pythagoras/d/IMatrix4.java
@@ -247,6 +247,21 @@ public interface IMatrix4
      */
     Vector3 transformVector (IVector3 vector, Vector3 result);
 
+    /**
+     * Transforms {@code vector} by this matrix (M * V).
+     *
+     * @return a new vector containing the result.
+     */
+    Vector4 transform (IVector4 vector);
+
+    /**
+     * Transforms {@code vector} by this matrix (M * V) and stores the result in the object
+     * provided.
+     *
+     * @return a reference to the result vector, for chaining.
+     */
+    Vector4 transform (IVector4 vector, Vector4 result);
+
     /**
      * Extracts the rotation component of the matrix.
      *
diff --git a/src/main/java/pythagoras/d/IVector4.java b/src/main/java/pythagoras/d/IVector4.java
index 3f77eb3..521383f 100644
--- a/src/main/java/pythagoras/d/IVector4.java
+++ b/src/main/java/pythagoras/d/IVector4.java
@@ -34,4 +34,18 @@ public interface IVector4
      * Compares this vector to another with the provided epsilon.
      */
     boolean epsilonEquals (IVector4 other, double epsilon);
+
+    /**
+     * Multiplies this vector by a matrix (V * M).
+     *
+     * @return a new vector containing the result.
+     */
+    IVector4 mult (IMatrix4 matrix);
+
+    /**
+     * Multiplies this vector by a matrix (V * M) and stores the result in the object provided.
+     *
+     * @return a reference to the result vector, for chaining.
+     */
+    IVector4 mult (IMatrix4 matrix, Vector4 result);
 }
diff --git a/src/main/java/pythagoras/d/Matrix4.java b/src/main/java/pythagoras/d/Matrix4.java
index 8d53d0d..9bf73cc 100644
--- a/src/main/java/pythagoras/d/Matrix4.java
+++ b/src/main/java/pythagoras/d/Matrix4.java
@@ -916,6 +916,20 @@ public final class Matrix4 implements IMatrix4, Serializable
                           m02*vx + m12*vy + m22*vz);
     }
 
+    @Override // from IMatrix4
+    public Vector4 transform (IVector4 vector) {
+        return transform(vector, new Vector4());
+    }
+
+    @Override // from IMatrix4
+    public Vector4 transform (IVector4 vector, Vector4 result) {
+        double vx = vector.x(), vy = vector.y(), vz = vector.z(), vw = vector.w();
+        return result.set(m00*vx + m10*vy + m20*vz + m30*vw,
+                          m01*vx + m11*vy + m21*vz + m31*vw,
+                          m02*vx + m12*vy + m22*vz + m32*vw,
+                          m03*vx + m13*vy + m23*vz + m33*vw);
+    }
+
     @Override // from IMatrix4
     public Quaternion extractRotation () {
         return extractRotation(new Quaternion());
diff --git a/src/main/java/pythagoras/d/Vector4.java b/src/main/java/pythagoras/d/Vector4.java
index 646edec..90fa042 100644
--- a/src/main/java/pythagoras/d/Vector4.java
+++ b/src/main/java/pythagoras/d/Vector4.java
@@ -92,6 +92,15 @@ public class Vector4 implements IVector4, Serializable
         return this;
     }
 
+    /**
+     * Multiplies this vector by a matrix (V * M) and stores the result back in this vector.
+     *
+     * @return a reference to this vector, for chaining.
+     */
+    public IVector4 multLocal (IMatrix4 matrix) {
+        return mult(matrix, this);
+    }
+
     @Override // from IVector4
     public double x () {
         return x;
@@ -125,6 +134,24 @@ public class Vector4 implements IVector4, Serializable
                 Math.abs(w - other.w()) < epsilon);
     }
 
+    @Override // from IVector4
+    public IVector4 mult (IMatrix4 matrix) {
+        return mult(matrix, new Vector4());
+    }
+
+    @Override // from IVector4
+    public IVector4 mult (IMatrix4 matrix, Vector4 result) {
+        double m00 = matrix.m00(), m10 = matrix.m10(), m20 = matrix.m20(), m30 = matrix.m30();
+        double m01 = matrix.m01(), m11 = matrix.m11(), m21 = matrix.m21(), m31 = matrix.m31();
+        double m02 = matrix.m02(), m12 = matrix.m12(), m22 = matrix.m22(), m32 = matrix.m32();
+        double m03 = matrix.m03(), m13 = matrix.m13(), m23 = matrix.m23(), m33 = matrix.m33();
+        double vx = x, vy = y, vz = z, vw = w;
+        return result.set(m00*vx + m01*vy + m02*vz + m03*vw,
+                          m10*vx + m11*vy + m12*vz + m13*vw,
+                          m20*vx + m21*vy + m22*vz + m23*vw,
+                          m30*vx + m31*vy + m32*vz + m33*vw);
+    }
+
     @Override
     public String toString () {
         return "[" + x + ", " + y + ", " + z + ", " + w + "]";
diff --git a/src/main/java/pythagoras/f/IMatrix4.java b/src/main/java/pythagoras/f/IMatrix4.java
index 4373509..7df310c 100644
--- a/src/main/java/pythagoras/f/IMatrix4.java
+++ b/src/main/java/pythagoras/f/IMatrix4.java
@@ -247,6 +247,21 @@ public interface IMatrix4
      */
     Vector3 transformVector (IVector3 vector, Vector3 result);
 
+    /**
+     * Transforms {@code vector} by this matrix (M * V).
+     *
+     * @return a new vector containing the result.
+     */
+    Vector4 transform (IVector4 vector);
+
+    /**
+     * Transforms {@code vector} by this matrix (M * V) and stores the result in the object
+     * provided.
+     *
+     * @return a reference to the result vector, for chaining.
+     */
+    Vector4 transform (IVector4 vector, Vector4 result);
+
     /**
      * Extracts the rotation component of the matrix.
      *
diff --git a/src/main/java/pythagoras/f/IVector4.java b/src/main/java/pythagoras/f/IVector4.java
index f6344ec..ea91fa4 100644
--- a/src/main/java/pythagoras/f/IVector4.java
+++ b/src/main/java/pythagoras/f/IVector4.java
@@ -34,4 +34,18 @@ public interface IVector4
      * Compares this vector to another with the provided epsilon.
      */
     boolean epsilonEquals (IVector4 other, float epsilon);
+
+    /**
+     * Multiplies this vector by a matrix (V * M).
+     *
+     * @return a new vector containing the result.
+     */
+    IVector4 mult (IMatrix4 matrix);
+
+    /**
+     * Multiplies this vector by a matrix (V * M) and stores the result in the object provided.
+     *
+     * @return a reference to the result vector, for chaining.
+     */
+    IVector4 mult (IMatrix4 matrix, Vector4 result);
 }
diff --git a/src/main/java/pythagoras/f/Matrix4.java b/src/main/java/pythagoras/f/Matrix4.java
index 2dff095..5a0f8f2 100644
--- a/src/main/java/pythagoras/f/Matrix4.java
+++ b/src/main/java/pythagoras/f/Matrix4.java
@@ -916,6 +916,20 @@ public final class Matrix4 implements IMatrix4, Serializable
                           m02*vx + m12*vy + m22*vz);
     }
 
+    @Override // from IMatrix4
+    public Vector4 transform (IVector4 vector) {
+        return transform(vector, new Vector4());
+    }
+
+    @Override // from IMatrix4
+    public Vector4 transform (IVector4 vector, Vector4 result) {
+        float vx = vector.x(), vy = vector.y(), vz = vector.z(), vw = vector.w();
+        return result.set(m00*vx + m10*vy + m20*vz + m30*vw,
+                          m01*vx + m11*vy + m21*vz + m31*vw,
+                          m02*vx + m12*vy + m22*vz + m32*vw,
+                          m03*vx + m13*vy + m23*vz + m33*vw);
+    }
+
     @Override // from IMatrix4
     public Quaternion extractRotation () {
         return extractRotation(new Quaternion());
diff --git a/src/main/java/pythagoras/f/Vector4.java b/src/main/java/pythagoras/f/Vector4.java
index 81ca86e..d8c53f5 100644
--- a/src/main/java/pythagoras/f/Vector4.java
+++ b/src/main/java/pythagoras/f/Vector4.java
@@ -92,6 +92,15 @@ public class Vector4 implements IVector4, Serializable
         return this;
     }
 
+    /**
+     * Multiplies this vector by a matrix (V * M) and stores the result back in this vector.
+     *
+     * @return a reference to this vector, for chaining.
+     */
+    public IVector4 multLocal (IMatrix4 matrix) {
+        return mult(matrix, this);
+    }
+
     @Override // from IVector4
     public float x () {
         return x;
@@ -125,6 +134,24 @@ public class Vector4 implements IVector4, Serializable
                 Math.abs(w - other.w()) < epsilon);
     }
 
+    @Override // from IVector4
+    public IVector4 mult (IMatrix4 matrix) {
+        return mult(matrix, new Vector4());
+    }
+
+    @Override // from IVector4
+    public IVector4 mult (IMatrix4 matrix, Vector4 result) {
+        float m00 = matrix.m00(), m10 = matrix.m10(), m20 = matrix.m20(), m30 = matrix.m30();
+        float m01 = matrix.m01(), m11 = matrix.m11(), m21 = matrix.m21(), m31 = matrix.m31();
+        float m02 = matrix.m02(), m12 = matrix.m12(), m22 = matrix.m22(), m32 = matrix.m32();
+        float m03 = matrix.m03(), m13 = matrix.m13(), m23 = matrix.m23(), m33 = matrix.m33();
+        float vx = x, vy = y, vz = z, vw = w;
+        return result.set(m00*vx + m01*vy + m02*vz + m03*vw,
+                          m10*vx + m11*vy + m12*vz + m13*vw,
+                          m20*vx + m21*vy + m22*vz + m23*vw,
+                          m30*vx + m31*vy + m32*vz + m33*vw);
+    }
+
     @Override
     public String toString () {
         return "[" + x + ", " + y + ", " + z + ", " + w + "]";