Fluorescence microscopy has become the most important physical phenomenon in modern biology and medicine. After a slow start, the possibility of specific fluorescence staining boosted this application in the early 30's of the last century. Around 1950 a second stage was ignited with the invention of immunofluorescent staining. Functional imaging, most prominently by Ca++ probes, delivered the method from the restraint to stick to morphological and structural imaging. The possibility to create living material with targeted expressible fluorescent proteins revolutionized fluorescence microscopy in an unexpected and extensive third stage. Currently, new methods that use specific fluorescent protein-features, are popping up weekly. And last but not least: all modes of super-resolution imaging are based on fluorescence.