The general picture we have of membranes and of the properties of the proteins imbedded in them, has, arguably emerged directly from probe studies over the past 20 years. This work is designed to make these techniques accessible to a board audience of cell biologists. The techniques discussed revolve primarily around the fluorescence of membrane probes, but applications of light absorption and Raman scattering are included. In addition to reviews of the major applications, most chapters include information on the required apparatus, experimental design, data analysis, and potential pit falls.