Introduction -- Feynman diagrams in quantum/statistical mechanics -- Real scalar fields and the renormalizations group -- Complex scalar fields -- Liquid ⁴He -- Bose-Einstein condensation of trapped ultracold atoms -- The electron gas -- Nuclear matter -- Cooper pairing and the BCS theory of superconductivity -- Pairing in liquid ³He and in nuclear matter -- Vortices and topological matter -- Strongly coupled fermionic gases -- Numerical evaluation of path integrals -- Quantum field theories on the lattice and supercomputers -- Theory of quark-gluon plasma -- Quark-gluon plasma in experiment -- The QCD vacuum I. Monopoles and confinement -- The QCD vacuum II. Chiral symmetries and their breaking -- Chiral matter -- Cold quark matter and color superconductivity -- The QCD vaccum III: Instanton-dyons -- Parting comments.