These are the lecture notes from a two-semester graduate course and a two-semester undergraduate course taught by the author. The lectures are arranged in a logical manner and reflect the informality of the classroom. Each topic is explained with several examples so that the ideas develop naturally, which is immensely helpful to students. The book is self-contained; most of the steps in the development of the subject are derived in detail and integrals are either evaluated or listed when needed. The motivated student can work through the notes independently and without difficulty. The book is suitable for graduate students in mathematics or advanced undergraduates in physics interested in an introduction to quantum mechanics.