Design and prototyping of an Inherently cOmpliant light-Weight Active hand prosthesis (called the IOWA hand) is presented. The hand has five actuated fingers, four with two joints and the thumb with three joints. Each joint is designed using a novel flexible mechanism based on the loading of a compression spring in both transverse and axial directions and using cable-conduit systems. The rotational motion is transformed to tendon-like behavior, which enables the location of the actuators far from the arm (e.g., on a belt around the waist). The forward kinematics of the mechanism is also presented and lends itself well for computer control. It is shown that the solution of the transverse deflection of each finger segment is obtained in a general form, while the stiffness coefficients are obtained in closed form with small deflection angles and for the large angles we use FEM to solve it. A prototype finger is experimentally tested, the results verified, and the hand prosthesis is built.