The study of quantum mechanics and its applications occupies a central position in the physical sciences, forming the basis for an understanding of atomic, molecular, nuclear, particle and condensed matter physics. The purpose of this book is to provide a core text in quantum mechanics for students of physics at the undergraduate level. It gives a modern, comprehensive introduction to the principles of quantum mechanics, to the main approximation methods and to the application of quantum theory to a wide variety of systems. The needs of students having an average mathematical ability are kept very much in mind, with the avoidance of complex mathematical arguments and any undue compression of material.  The text is illuminated throughout by careful explanation and physical insight. Problem sets, which cover all the main topics, reinforce the student's understanding and act as a guide to progress.