The main content of this book is an introduction to Yang-mills fields and the standard model of particle physics. A concise introduction to quarks is provided, with a discussion of the representations of SU(3). The standard model is presented in detail, including such topics as the Kobayashi-Maskawa matrix, chiral symmetry breaking and the omega-vacuum. Theoretical topics of a more general nature include path integrals, topological solitons, renormalization group, effective potentials, the axial anomaly and lattice gauge theory. This second edition has been expanded and includes Wilson's renormalization scheme, and its relation to perturbative renormalization; pitfalls in quantizing gauge fields, such as the Gribov ambiguity; the lattice as a consistent regularization; Monte Carlo methods of solution; and the issues, folklores and scenarios of quark confinement.