Professor Stefan Hell is Director at the Max Planck Institute for Multidisciplinary Sciences in Göttingen and the Max Planck Institute for Medical Research in Heidelberg. He earned his PhD in Physics from the University of Heidelberg and is internationally recognised as a pioneer in optical microscopy. Hell revolutionised the field by developing super-resolution fluorescence microscopy techniques that overcome the diffraction limit of light, enabling imaging at nanometer-scale resolution. For these achievements, he was awarded the Nobel Prize in Chemistry in 2014. Hell's group is developing light microscopes with a spatial resolution down to a few nanometers, particularly for imaging cells and tissue of a living organism. Prominent methods include STED and RESOLFT microscopy as well as concepts based on stochastic single-molecule switching such as GSDIM microscopy. To surpass the diffraction barrier, all these methods utilise a reversible transition or switch of fluorescent labels between a bright and a dark state. In combination with 4Pi microscopy, the resolution can be increased in all spatial dimensions down to the nanometer scale. Consequently, the group also pioneers the chemical synthesis and application of new labelling methods and techniques to improve the performance of the labels’ switching behaviour to separate close-by molecules.