In the nearly 45 years since Stan Ovshinsky's original publication [Phys. Rev. Lett. 21, 1450 (1968)] announcing the discovery of electric-field-induced threshold switching in chalcogenide alloy semiconductor glass thin films, the field of amorphous semiconductor physics has developed remarkably. Many commercial applications of these materials have been developed, including X-ray image intensifiers, photocopier photoreceptors, and optical and electrical phase change memory devices. Despite these developments, a universally agreed upon, comprehensive model for the Ovshinsky Effect threshold switch still has not emerged. This paper is a brief review of the present state of understanding of this fascinating solid state physics phenomenon.