On the 11th and 12th of May 2017 the CRC organised its 4th international symposium with the title of “Microbial and Cellular Communities in Infection”. The venue of the old town hall provided international participants with a perfect setting that best represents the traditions and history of Hannover. Invited speakers and CRC scientists presented their newest results and then discussed them with the audience. To close the symposium the guests were invited to a guided tour of the Herrenhausen Gardens followed by dinner in the Herrenhausen Palace kitchen restaurant and a musical performance of baroque songs provided by an opera singer accompanied on the piano.