The ankle joint prosthesis adapted to involve the patient's distal tibia and talus has, according to the present invention, tibial, talar and mobile or semi-constrained bearing components that are laterally to medially implanted in the patient. The tibial component's top surface has convex curvature in its anterior to posterior plane and is configured so as to approximate and match with the curvature of a prepared portion of the distal tibia; its bottom surface being approximately flat. The talar component's top surface has saddle-shaped, convex curvature in its anterior to posterior plane, it's bottom surface has concave curvature and is configured so as to approximate and match with the curvature of a prepared portion of the talus. The mobile or semi-constrained bearing components have embodiments that comprise a wide variety of geometric shapes. A method for implanting such a prosthesis is also disclosed.