Below-knee amputation is one of the most frequently performed types of amputation in the United States. This paper describes CamWalk, a novel passive ankle prosthesis that has mechanical behavior similar to that of a natural ankle. CamWalk generates rotational push-off to propel the walker forward using a compliant coupling between two degrees-of-freedom (DOFs) (deflection along the leg and rotation about the ankle). The design closely matches the ankle torque and ankle work characteristics of an average healthy ankle. Simulation results indicate that CamWalk generates 44.5% of the net rotational work performed by a natural healthy ankle when leg deflection is limited to 15 mm. Standard gait analysis of four amputees using CamWalk demonstrated that the device performance ranged from marginally dissipative to significantly active, generating 48.0% of the work performed by their natural ankle.