This Problem Book is based on the exercises and lectures which I have given to undergraduate and graduate students of the Faculty of Physics, University of Belgrade over many years. Nowadays, there are a lot of excellent Quantum Field Theory textbooks. Unfortunately, there is a shortage of Problem Books inthis?eld, oneoftheexceptionsbeingtheProblemBookofChengandLi 7]. The overlap between this Problem Book and 7] is very small, since the latter mostly deals with gauge ?eld theory and particle physics. Textbooks usually contain problems without solutions. As in other areas of physics doing...