Abstract: A robot leg (125) comprises an upper link (101) and a lower link (111). The upper link (101) operates nominally in a first vertical plane, for example the sagittal plane, while the lower link (111) operates nominally in a second vertical plane, nominally orthogonal to the first plane, for example the coronal plane. The leg (125) may also comprise a twist joint in the knee, and may comprise four-bar linkages (102a-b, 103a-d, 112a-b, 113a-d), such that the foot (106) stays parallel to the hip (102a). The leg (125) may be used in a robot to allow the construction of a robot capable of three dimensional movement, using a small number of actuators per leg.