Providing a broad review of many techniques and their application to condensed matter systems, this book begins with a review of #thermodynamics and #statistical_mechanics, before moving onto real and imaginary time path integrals and the link between Euclidean quantum mechanics and statistical mechanics. A detailed study of the #Ising, #gauge-Ising and #XY models is included. The #renormalization group is developed and applied to #critical_phenomena, #Fermi_liquid theory and the renormalization of field theories. Next, the book explores bosonization and its applications to one-dimensional fermionic systems and the correlation functions of homogeneous and random-bond Ising models. It concludes with Bohm-Pines and Chern-Simons theories applied to the quantum Hall effect. Introducing the reader to a variety of techniques, it opens up vast areas of condensed matter theory for both graduate students and researchers in theoretical, statistical and condensed matter physics.