There is contemporary research interest in the development of second-order nonlinear optical materials exhibiting large first hyperpolarizabilities (β) for possible applications in electro-optic devices. In this article, the structure–property relationships of octupolar molecules such as tris(bipyridyl) metal ion complexes and 1,3,5-trisubstituted benzene, triphenylamine, 1,3,5-trimethoxybenzene, subphthalocyanine, truxenone, 1,3,5-trinitrobenzene, 1,3,5-triazine, 1,3,5-tricyanobenzene, and hexasubstituted benzene derivatives are briefly reviewed to provide a guideline for the design of efficient nonlinear optical materials.