Thin films of organic nonlinear optical materials have become of increasing interest for potential electro-optic and nonlinear optical applications. Organic molecular layer deposition (OMLD) consists of an alternating evaporation of suitable difunctional monomers under UHV conditions and allows self-terminating monolayer growth and in-situ polymerization of periodic structures. Film stability is increased due to chemical bonding between the alternating layers. Moreover, in contrast to epitaxial growth techniques, the choice of interesting inorganic substrates is not limited by lattice-matching conditions. We have investigated the xperimental requirements for OMLD in detail, with pyromellitic acid dianhydride (PAD), terephthalic acid dichloride (TOC), and 4,4′-diamino-diphenylether (DDE) as prototype precursors. After optimization of material fluxes and growth temperatures, covalently bonded monolayers were formed via a self-terminating surface reaction while excessive material was desorbed.