This textbook presents various methods to deal with quantum many-body systems, mainly addressing interacting electrons. It focusses on basic tools to tackle quantum effects in macroscopic systems of interacting particles, and on fundamental concepts to interpret the behavior of such systems as revealed by experiments.The textbook starts from simple concepts like second quantization, which allows one to include the indistinguishability and statistics of particles in a rather simple framework, and linear response theory. Then, it gradually moves towards more technical and advanced subjects,...