INTRODUCTIONThis article describes imaging techniques using single optical labels, ranging from fluorescent dyes to scattering particles, for the study of the movement of individual or small assemblies of membrane proteins. These techniques have been used to track the movements of different types of plasma membrane proteins, such as neurotransmitter receptors and adhesion proteins. They can be used to probe the degree of interaction between membrane proteins and cytoplasmic stabilizing elements in live cells.