Ground state depletion (GSD) microscopy is a form of super-resolution light microscopy suggested almost a decade ago but demonstrated practically in 2007. In principle, this is a parallel recording wide-field approach that temporarily switches the majority of fluorophores off to allow the precise localization of single fluorophores. Almost all fluorophores in the sample are turned dark by high-intensity laser excitation, leaving only single, well-separated fluorophores emitting fluorescence. The precise localization of the fluorescent dyes is then determined to produce images with a resolution in the 20- to 50-nanometer range. One of the key advantages of this method over other localization techniques is that it can be used with standard fluorescence labels routinely applied in biomedical research.