Lectures on the Theory of the Weak Interaction

I review aspects of the theory of the weak interaction in a set of lectures originally presented at the 2016 CERN-JINR European School of Particle Physics. The topics discussed are: (1) the experimental basis of the V-A structure of the weak interaction; (2) precision electroweak measurements at the Z resonance; (3) the Goldstone Boson Equivalence Theorem; (4) the Standard Model theory of the Higgs boson; (5) the future program of precision study of the Higgs boson.