Following brief review of applications of the Ornstein-Zernike equation for bulk fluids, singlet and pair Ornstein-Zernike equations are formulated for inhomogeneous fluids in which the density is no longer uniform. The singlet theory can be accurate and is quite easy to use. However, its deficiencies appear in wetting problems and in coulomb fluids near highly charged electrodes. The pair theory has been successful in all its applications to date and, in addition, yields information about the pair correlation functions of inhomogeneous fluids that is lacking in most other approaches. © 1988 American Chemical Society.