Theoretical guidance, provided by quantum and statistical mechanical calculations, has aided the recent realization of electro-optic coefficients of greater than 300 pm/V (at 1.3 microns wavelength). This articles attempts to provide physical insight into those recent results and to explore avenues for the further improvement of electro-optic activity by structural modification, including to values of 500 pm/V and beyond. While large electro-optic coefficients are a necessary condition for extensive practical application of organic electro-optic materials, they are not a sufficient condition. Adequate thermal and photochemical stability, modest to low optical loss, and processability are important additional requirements. This article also examines such properties and suggests routes to achieving improved auxiliary properties.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.