Some organic crystalline solids that comprise highly polar molecules and that form non-centrosymmetric crystal structures exhibit second-order nonlinear optical properties and laser-damage thresholds that are potentially superior to those of currently available inorganic systems. This realization has led to a search for organic materials with improved properties and also to the consideration of organic crystals as active components in optical and optoelectronic device systems. Empirical and theoretical attempts have been made to predict novel molecules, which when synthesized might form, or be engineered to form, non-centrosymmetric crystals of even greater potential than the known systems. In parallel, efforts have been made to grow high quality, optically perfect, single crystals for the evaluation of the optical properties and device potential of this class of material. Data obtained on the resulting range of materials and crystals serve to confirm this potential.