This book is concerned with the practical aspects of solving angular momentum problems. The novel but fully tested-out method (the Invariant Graph Method) allows one to write down from a single graph the complete final result of the problem. The drawing of the graph involves very few simple, essentially self-evident rules. Still it is a powerful tool to easily solve the most involved physical problems.The method is introduced step-by-step in a sequence of examples, beginning with the simplest matrix elements, and ending with the most general case of a reaction including angular distributions and correlations. The many-body and particle anti-particle systems are fully developed. All aspects: wave functions, vectors, operators, Fock space state vectors and operators, etc., are treated on the same footing. All concepts of angular momentum theory acquire a transparent meaning. Hence the book is valuable not only as a handbook in problem solving, but extremely so as an adjunct in any course on advanced qunatum physics, atomic, molecular, nuclear and particle physics.