As optical technology becomes poised to revolutionise the world of communication the need for novel nonlinear optic (NLO) and electrooptic (EO) materials is increasing rapidly. NLO and EO materials come in many shapes and sizes; there are the large, aesthetically-pleasing, optically perfect and well known inorganic single crystals such as lithium niobate (LiNbo3), and the less familiar potassium titanyl phosphate(KTiOPO4 or KTP) and β-barium borate (β-BaB2O4 or BBO). There are also crystalline thin films, organic polymer or composite thin films and transparent inorganic ceramics such as lead lanthanum zirconium titanate (PLZT) I will concentrate here on the wide range of research on inorganic, dielectric single crystals.