At optical and infrared wavelengths, imaging Fabry-Perot devices are used in three different ways: (i) to obtain a single spectrum of a diffuse source which fills a large fraction of the aperture, (ii) to obtain a monochromatic image within a field defined by the Jacquinot spot, and (iii) to obtain a spectrum at each pixel position over a wide field by tuning the etalon. We review the theoretical basis for Fabry-Perot photometry and summarize the calibration procedures for the different applications. We discuss methods for recognizing and dealing with artefacts (scattered light, atmospheric effects, etc.) which can seriously comprise the photometric integrity of the data if left untreated.