Polymeric films fabricated from ionically self-assembled monolayers (ISAMs) spontaneously from in a noncentrosymmetric structure requisite for a nonzero second order nonlinear optical (NLO) susceptibility, (chi) (2), without the need for electric field poling. ISAM NLO films exhibit excellent long-term temporal stability of (chi) (2), having shown no decay over a period of nearly three years. They are also remarkably stable at elevated temperatures. While (chi) (2) decreases by 20 percent as the temperature is raised to 150 degrees C, total recovery of the susceptibility is observed upon cooling, demonstrating that the decrease is not due to an irreversible randomization of the chromophore alignment. The thickness, orientational order, and NLO response are found to be strongly dependent on the pH and ionic strength of the solutions form which the films are deposited. The largest (chi) (2) values are observed in films with the smallest bilayer thickness. This suggests that polar orientation is obtained primarily at the interfaces between adjacent layers rather than throughout a full monolayer.