Atomic layer deposition (ALD) has gained attention by allowing for nanoscale control of inorganic films via a sequence of self-limiting surface reactions.  In an analogous technique, nanoscale organic thin films are deposited by molecular layer deposition (MLD), utilizing a series of self-limiting reactions of organic molecules.  In this study, 1,4-phenylene diisocyanate (PDIC) and ethylenediamine (ED) are employed to deposit polyurea films on a silicon substrate.  3-aminopropyltriethoxysilane is vapor deposited on the hydroxylated SiO₂ surface to yield an amine-terminated surface, as confirmed by ellipsometry and XPS.  Following amine termination, PDIC and ED are dosed in a binary cycle, and this cycling is repeated to yield the desired thickness of organic film.  Ellipsometry and SEM indicate a linear growth rate of 6.7 Ĺ/cycle, with each of the reactants demonstrating saturation behavior with increasing exposure time.  The urea coupling moiety is confirmed by FT-IR, and films are shown to have stoichiometric composition by XPS.  Temperature dependent measurements show that the films have good thermal stability.  Density function theory is used to elucidate the reaction pathway and predicts an estimated growth rate of 6.4 Ĺ/cycle.   Experimental and theoretical studies of related MLD systems, including combinations of diisocyanates and diisothiocyanates with diols, dithiols, and diamines, will also be presented.