The concept of symmetry will play a crucial role in nearly all aspects of our discussion of weak interactions. At the level of the dynamics, the fundamental interactions (or at least that subset of the fundamental interactions that we understand) are associated with "gauge symmetries". But more than that, the underlying mathematical language of relativistic quantum mechanics — quantum field theory — is much easier to understand if you make use of all the symmetry information that is available. In this course, we will make extensive use of symmetry as a mathematical tool to help us understand the physics. In particular, we make use of the language of representations of Lie algebras.