Covers both the basic concepts and theory behind the various FRET microscopy and spectroscopy techniques, and the practical aspects of using the techniques and analyzing the results. The critical tricks for obtaining a good FRET image and precisely quantitating the signals from living specimens at the nanomolecular level are explained. Valuable information about the preparation of biological samples used for FRET image analysis is also provided. The methods covered include different types of microscopy systems and detectors (wide-field, confocal, multi-photon) as well as specialized techniques such as photobleaching FRET, FLIM-FRET microscopy, spectral imaging FRET, single molecule FRET, and time and image correlation spectroscopy. Starting from the basics, the chapters guide readers through the choice of probes to be used for FRET experiments and the selection of the most suitable experimental approaches to address specific biological questions.