The „Ernst Haeckel (1834-1919): Briefedition‟ is a long-term project funded by the Union of the German Academies of Sciences and is supervised by the German Academy of Natural Scientists Leopoldina - National Academy of Sciences. It is situated at the Ernst-Haeckel-House in the Friedrich Schiller University of Jena. The project consists of two modules, a 25-volume print edition (Ernst Haeckel: Selected correspondence. Historical-critical edition. Stuttgart 2017 ff.), as well as a complete online edition. The online edition will provide all of Haeckel's correspondence (with full texts and metadata) by 2037.