Total internal reflection fluorescence (TIRF) microscopy (also called ‘evanescent wave microscopy’) provides a means to selectively excite fluorophores in an aqueous or cellular environment very near a solid surface (within #100 nm) without exciting fluorescence from regions farther from the surface. Fluorescence excitation by this thin zone of electromagnetic energy (called an ‘evanescent field’) results in images with very low background fluorescence, virtually no out-offocus fluorescence, and minimal exposure of cells to light at any other planes in the sample. The unique features of TIRF have enabled numerous applications in biochemistry and cell biology.