Fiji is an image processing package—a “batteries-included” distribution of ImageJ, bundling a lot of plugins which facilitate scientific image analysis. Fiji is easy to install and has an automatic update function, bundles a lot of plugins and offers comprehensive documentation. Fiji is an open source project hosted in a Git version control repository, with access to the source code of all internals, libraries and plugins, and eases the development and scripting of plugins. Fiji is licensed under the GNU General Public License. It builds on top of the ImageJ2 core, which is licensed under the permissive BSD 2-clause license. Plugins and other components have their own licenses. Fiji is developed by contributors around the world, and funded from various sources. It is maintained by Curtis Rueden and the ImageJ development team at the Laboratory for Optical and Computational Instrumentation (LOCI) at the University of Wisconsin-Madison.