This book provides the reader with an explanation of the origin and establishment of quantum mechanics, with the mathematics in a digestible form, together with a descriptive survey of later developments up to the present day. The mathematical treatment closely follows the original treatment, but in modern terms, using uniform symbolism as much as possible and with simplifications (e.g. the use of one dimension instead of three) to avoid unnecessarily complicated-looking mathematics.Containing an extensive bibliography and useful appendices as well as references to original works, reviews, and biographies, the reader is well-equipped to delve further into the subject. In addition to its importance for those studying physics, it is also valuable for those studying the history of science.