Achieving motion control at the molecular level including solid-state and surface-mounted rotors, and their natural progression to the development of synthetic molecular machines. In addition to an analysis of the design principles used to control linear and rotary motion in these molecular systems, this review will address advances towards the construction of synthetic machines that can perform useful functions. Approaches adopted by various research groups to construct fully synthetic molecular machines and devices are compared. This is illustrated with molecular rotors, elevators, valves, transporters, muscles and other motor functions used to develop intelligent materials. The demonstration of molecular machinery stands out through recent examples of systems capable of effecting macroscopic motion through a concerted molecular movement. Several approaches are discussed to illustrate how molecular motor systems have been used to perform the work. We will conclude with perspectives of future developments in this exciting field of nanotechnology.