Quantization I; II", Ann. Phys. 111 (1978) 61-110; 111-151, Bayen, Flato, Fronsdal, Lichnerowicz and Sternheimer showed that quantum theory could be approached as a deformation of classical mechanics. This raised numerous questions including, e.g., whether any Poisson manifold could be quantized (subsequently proven by Kontsevich). This talk will outline the ideas in the original paper and some of the subsequent developments.