Topics: Fick'S Law, Brownian Motion, Langevin Equation, Correlation Functions and Inelastic Scattering, Isolated Diffusion Mechanisms on Surfaces, Collective Diffusion Processes on Surfaces, Surface Vibrations, Analytic and Computational Approaches to Calculating Hopping Rates. the Role of Friction in Microscopic Surface Dynamics. Measurements of Surface Motion Using Optical and Electron Spectroscopy, Scattering Tunneling Microscopic, Field Ion Microscopy, Neutron Scattering Atomic and Molecular Scattering and Thermal Desorption. Measuring Non-Equilibrium Surface Dynamics.