During the years 1987 to 1990, the flora and vegetation of the calcareous fens of the Main-Kinzig-Kreis which had become known to the authors were investigated. The Cratoneuretum commutati, the Molinietum caeruleae caricetosum hostianae and a basic community of the Caricion davallianae were identified as the characteristic plant communities and documented by vegetation releves. 31 calcareous fen areas are described. Advice is given on the cultivation and management of 21 sites where the characteristic vegetation continues to exist. The present main source of endangerment is the abandonment of agricultural utilization.