Not to be confused with Langenhessen, which is 2 km north of Werdau.Langen is a town of roughly 36,000 in the Offenbach district in the Regierungsbezirk of Darmstadt in Hesse, Germany. The town is between Darmstadt and Frankfurt am Main and part of the Frankfurt Rhein-Main urban area. Langen is headquarters to Deutsche Flugsicherung (German air traffic control), and is also home to the Paul-Ehrlich-Institut, a Federal serum- and vaccine-making institution.