This book is intended as a general introduction to modem physics for science and engineering students. It is written at a level which presumes a prior TUII year's course in classieal physics, and aknowledge of elementary differential and integral calculus. The material disc ussed here includes probability, relativity, quantum mechanics, atomic physics, statistical mechanics, nuclear physics and elementary particles. A number of topics, especially in quantum mechanics, are presented in greater depth than is customary, in many cases, unique ways of presentation are given which greatly simplify the discussion of there topics. However, few of the developments require more mathematics than elementary caleculus and the algebra of complex numbers; in a few places, familiarity with partial differentiation will be necessary.