Novel and simple methods, systems, and computer program products for implementing a 3D rotation using input from a mouse, trackball, or other input device are described. Methods of implementing rotations are presented which lead to new realizations of the 3D rotation group and its double-cover, the unit quaternions. New methods, systems, and computer program products are also presented for interpolating rotations of a 3D scene that is more efficient than previously-known quaternion-based methods. The new methods are also used to derive the quaternion composition formula from the geometry of 3D rotations.