The book is intended for those who are familiar with basic facts from classical and quantum mechanics as well as from statistical physics. We would like to stress that the book is not just a linearly ordered set of facts about path integrals and their applications, but the reader may find more effective ways to learn a desired topic. Each chapter is self-contained and can be considered as an independent textbook: it contains general physical background, the concepts of the path-integral approach used, followed by most of the typical and important applications presented in detail. In writing this book, we have endeavored to make it as comprehensive as possible and to avoid statements such as 'it can be shown' or 'it is left as an exercise for the reader', as much as it could be done.