A prosthetic ankle has an ankle joint body (10A) constituting a shin component and a foot component (12). The ankle joint body (10A) is pivotally connected to the foot component (12) by a first pivotal connection (14) defining a medial-lateral ankle joint flexion axis. The ankle joint body (10A) also forms the cylinder of an ankle joint piston and cylinder assembly with a superior-inferior central axis, the cylinder housing a piston (16) with upper and lower piston rods (16A, 16B). The lower piston rod (16B) is pivotally connected to the foot component (12) at a second pivotal connection (18). As the ankle joint body (10A) pivots about the ankle joint flexion axis, the piston (16) moves substantially linearly in the cylinder formed by the ankle joint body. The cylinder is divided into upper and lower chambers (20A, 20B). These chambers are linked by an hydraulic circuit (22) incorporating passages (22A, 22B) in the ankle joint body (10A), and an energy conversion device in the form of a slave piston and cylinder assembly (24) having a piston (24P) and piston rods (24R) which project beyond the cylinder (24C) of the assembly (24).