Phase transitions and mean field theory, critical exponents and universality. Ginzburg-Landau theory: fluctuations, Ginzburg criterion, upper/lower critical dimensions, Goldstone modes. Renormalization group: Foundations, Perturbative RG, epsilon expansion, Large N expansion. XY model: Topological defects, Coulomb gas and Kosterlitz?Thouless transition. Nonlinear sigma models. Random Systems. Introduction to conformal invariance. Prerequisite: PHYSICS 602