Book excerpt: This textbook covers the main topics in contemporary condensed matter physics in a modern and unified way, using quantum field theory in the functional-integral approach. The book highlights symmetry aspects in acknowledging that much of the collective behaviors of condensed matter systems at low temperatures emerge above a nontrivial ground state, which spontaneously breaks the symmetry.The emphasis is on effective field theories which provide an efficient and powerful description that is valid at long wavelengths and low frequencies. In conjunction with the emphasis on effective theories, a modern approach towards renormalization is taken, whereby a wavenumber cut-off is introduced to set a scale beyond which the microscopic model under consideration ceases to be valid. The unique and innovative character of this presentation, free of historical constraints, allows for a compact and self-contained treatment of the main topics in contemporary condensed matter physics.