We report single-molecule observations of surfactant adsorption, desorption, and surface diffusion at the solid/solution interface using total internal reflection fluorescence microscopy (TIRFM). Typical surfactants used include carboxylic and phosphatidic acids; substrates include fused silica and single crystal sapphire. The observation of individual adsorption and desorption events permits the calculation of molecular "on rates" and "off rates" as a function of concentration, and their comparison to the net adsorption rate as measured by laterally-averaging techniques. The surface residence time distribution is also determined, and is consistent with first-order desorption kinetics. Surface trajectories of individual molecules are analyzed as a function of surface crowding, and analyzed with respect to two-dimensional Brownian motion. Typical surface diffusivities are in the range 0.01-0.1 square microns/second. Some interesting anomalies from ideal Brownian behavior are observed at long diffusion times.