An artificial joint (3), particularly for replacing a talocrural joint, including a first primary joint surface (1) that forms an articular fossa (4) particularly for replacing the tibia composed of concave curvatures extending parallel to a primary function plane of the joint (3), which corresponds to the sagittal plane, and a second primary joint surface (2) which cooperates with the first primary joint surface (1) as a component of a condoyle (5) that replaces the talus and has convex curvatures (7,8,9,10) on the primary function plane that are adapted to the first primary joint surface (1). To achieve high stress resistance and optimal joint mobility, depending on the position of the joint, the radii of the curvatures (7,8,9,10) are calculated such that the differential amounts arising between the corresponding radii of the first and second primary joint surfaces (1,2) in an ascending angular position (V) relative to a descending angular position and also simultaneously between a medial face (11) and a lateral face (12) of the joint (3) deviate from one another.