An improved artificial leg has a ball and socket ankle joint (3) connecting a foot (2) to a shin member (1). The ankle joint comprises a two-part socket (5A, 5B) enclosing a part-spherical ball member (4) with an elastic sleeve (6) sandwiched between the socket and the ball member (4) to allow resilient flexion of the foot (2) relative to the shin member (1). In order to provide relatively more resistance to dorsi-flexion than to plantar-flexion, an elastic buffer in the form of a ring (11) is disposed around a coupling shank portion (4A) of the ball member (4) to engage a downwardly extending anterior skirt portion (12) of the socket. In the preferred embodiment of the invention the skirt portion (12) also extends around each side of the ring (11) to provide resistance to medial and lateral flexion.