This book was written with the aim of providing an alternative to the postulatory approach currently used in many introductory quantum mechanics courses. Thus the first chapters are designed to familiarize the reader with the mathematical treatment and particular properties of ordinary wave motion which apply also to particle motion and have crucial importance to the subsequent development of the subject. The close relation of quantum theory to physical optics is stressed, and by use of Feynman's derivation of quantum mechanics, the wave theory for particles is made to appear as inevitable and necessary as Huygens wave theory for light.