Students of particle physics often find it difficult to locate resources to learn calculational techniques. Intermediate steps are usually not given in the research literature. To a certain extent, this is the case even in some of the established textbooks. In this book of worked problems enough details are provided so that the beginner will understand the solution in each particular case. With this step-by-step guidance, students (after first attempting the solution themselves) can develop their skills and confidence in their ability to work out particle theory problems. Besides being a problems/solutions addition to the well established textbook by Cheng & Li, this book introduces several new topics. It provides the reader with a self-contained approach to the subject, suitable even for those not familiar with the textbook. All problems have been given a descriptive title, enabling the reader to select according to his preferences.