A continuously variable transmission device has planetary members (23) in rolling contact with radially inner and outer races (12, 14; 36, 37) each comprising axially spaced relatively axially movable parts, and control means (18) for determining the axial separation of the parts (12, 14) of one of the two races, in which the planetary members (23) are connected for drive transmission to an input or output member (30) of the transmission device by connection means which allows the radial position of the planets to vary in response to variation in the axial separation of the parts (12, 14) of the said one of the two races (37), and in which the generatrix of the curved surface (70, 71) of at least one of the races (37) and/or planetary members (23) is non-circular.