Abstract Since 1996 the “Workgroup Odonata in North Rhine-Westphalia” (“AK Libellen NRW”) has built up a data base including about 150.000 data sets concerning the occurrence of dragonflies in North Rhine-Westphalia (NRW). This data confirms an increase and spread of some thermophilous dragonfly species in NRW, and the effects of climate change evidenced by an increasing average temperature, are considered to be important reasons for this process.