The molecular motor kinesin is a homodimer containing two heads-globular domains each of which has an ATP- and a microtubule-binding site. It is argued by analogy to other proteins with coiled-coil dimerization domains that the kinesin dimer has an approximate axis of rotational symmetry. The path kinesin follows along the surface of the microtubule is parallel to the protofilaments, and the steps are likely separated by 8 nm, the length of the tubulin dimer. Micromechanical recordings from single kinesin molecules indicate that one motor can exert a force as great as 5 pN. The efficiency of kinesin probably is in the order of 50%, considering the free energy available from ATP hydrolysis. Structural, mechanical, and biochemical experiments suggest that in order not to let go of a microtubule, the two heads of kinesin might move in a coordinated manner, perhaps undergoing a rotary motion.