Stefan W. Hell discusses the evolution of optical microscopy, particularly the breakthroughs that have overcome the diffraction limit. Traditionally, light microscopes could not resolve details finer than about half the wavelength of light due to diffraction. However, in the early 1990s, new concepts emerged that allowed for nanoscale resolution. These methods, such as STED, GSD, SPEM, RESOLFT, PALM, and STORM, use fluorescence switching to achieve resolutions below the diffraction limit. These techniques involve switching fluorophores on and off sequentially to resolve objects that are closer than the diffraction limit. The key to these methods is the use of molecular states, where fluorophores can switch between a fluorescent (on) state and a dark (off) state. By controlling these states, it is possible to localize individual molecules with high precision. There are two main approaches: targeted switching, where the spatial light intensity distribution is used to confine the fluorophore states, and stochastic switching, where molecules are randomly switched on and off. Targeted switching methods, such as STED and GSD, use structured illumination to confine the fluorophore states, while stochastic methods, like PALM and STORM, rely on the random activation and deactivation of individual molecules. Both approaches have their advantages and limitations, with targeted switching offering higher resolution but slower imaging, and stochastic switching allowing for faster imaging but requiring more complex data processing. The future of nanoscopy is promising, with ongoing developments in molecular switches and imaging techniques that could further enhance resolution and speed. The ability to achieve nanoscale resolution has significant implications for biological imaging, enabling the study of cellular structures and processes at an unprecedented level of detail.Stefan W. Hell discusses the evolution of optical microscopy, particularly the breakthroughs that have overcome the diffraction limit. Traditionally, light microscopes could not resolve details finer than about half the wavelength of light due to diffraction. However, in the early 1990s, new concepts emerged that allowed for nanoscale resolution. These methods, such as STED, GSD, SPEM, RESOLFT, PALM, and STORM, use fluorescence switching to achieve resolutions below the diffraction limit. These techniques involve switching fluorophores on and off sequentially to resolve objects that are closer than the diffraction limit. The key to these methods is the use of molecular states, where fluorophores can switch between a fluorescent (on) state and a dark (off) state. By controlling these states, it is possible to localize individual molecules with high precision. There are two main approaches: targeted switching, where the spatial light intensity distribution is used to confine the fluorophore states, and stochastic switching, where molecules are randomly switched on and off. Targeted switching methods, such as STED and GSD, use structured illumination to confine the fluorophore states, while stochastic methods, like PALM and STORM, rely on the random activation and deactivation of individual molecules. Both approaches have their advantages and limitations, with targeted switching offering higher resolution but slower imaging, and stochastic switching allowing for faster imaging but requiring more complex data processing. The future of nanoscopy is promising, with ongoing developments in molecular switches and imaging techniques that could further enhance resolution and speed. The ability to achieve nanoscale resolution has significant implications for biological imaging, enabling the study of cellular structures and processes at an unprecedented level of detail.