Gauge symmetry has become one of the most basic concepts in the theoretical framework for understanding fundamental interactions: The quantum field theories of the strong, weak, and electromagnetic interactions are all gauge invariant; general relativity can also be viewed as a classical gauge theory. This Resource Letter is intended for nonspecialists who wish to study gauge theories and their applications to elementary particle physics. About half of our discussion is devoted to the general properties of gauge‐invariant quantum field theories and half to their applications, from QED, QCD, and the Weinberg–Salam model to grand unification. The letter E after an item indicates elementary level or material of general interest to persons becoming informed in the field. The letter I, for intermediate level, indicates material of somewhat more specialized nature; and the letter A indicates rather specialized or advanced material. An asterisk (*) indicates those articles to be included in an accompanying Reprint Book.