The present text offers a graduate level treatment of time dependent phenomena in condensed matter physics. Conventional ideas of linear response theory and kinetic theory are treated in detail. The general emphasis, however, in on the development of generalized Langevin equations for treating nonlinear behaviour in a wide variety of systems. A full treatment is given for the underpinnings of hydrodynamics for fluids.This is the third volume of a four volume set of texts by the same author, two of which have already been published ("Fluctuations, Order, and Defects" 0-471-32840-5, "Equilibrium Statistical Mechanics" 0-471-32839-1). While the preceding volume contains material that is a prerequisite for fully understanding the material presented here, this volume is self-contained and can stand alone from the preceding volume.