This essential explains what distinguishes light sheet microscopy from ordinary light microscopy. The author briefly examines the history of such principles, focusing on the technical concepts. Finally, current manifestations are presented without descending into the depths of the art of engineering. The unusual feature of light-sheet microscopy is not only that observation and illumination take place at a right angle, but also that this type of microscopy gains in particular from the fact that the type of illumination only passes through a very small part of the specimen. The appropriate selection of optical elements ensures that the observed image no longer contains any blurred parts. This Springer essential is a translation of the original German 1st edition essentials, Die Lichtblattmikroskopie by Rolf Theodor Borlinghaus, published by Springer Fachmedien Wiesbaden GmbH, part of Springer Nature in 2017. The translation was done with the helpof artificial intelligence (machine translation by the service DeepL.com). A subsequent human revision was done primarily in terms of content, so that the book will read stylistically differently from a conventional translation. Springer Nature works continuously to further the development of tools for the production of books and on the related technologies to support the authors.