We discuss the possibility of manipulating the center-of-mass motion of molecules using the nonlinear interaction of a moderately intense, long-pulse laser field with the molecular polarizability tenser. Recent theoretical work demonstrating the possibility of focusing and trapping molecules is extended to consider the effects of circularly and elliptically polarized light and the effect of nonspherical laser optics. The aberrations affecting the quality of the "molecular lens" are analyzed and the means by which they can be minimized are discussed. Molecular focusing is extended to a general field of molecular optics; the possibilities of steering, reflecting, and collimating molecular beams are illustrated. Application of the mechanical force of light to disperse and separate species according to their mass, velocity, or quantum state is proposed. (C) 1997 American Institute of Physics.