In this preface, the editors present an overview of the topics and scope of the European Conference on Modelling Foundations and Applications (ECMFA), and describe the editorial and reviewing process for its 17th edition (ECMFA 2021).The papers selected for publication and presentation are presented and briefly described, as well as the details about the keynote talk by Prof. Jean-Marc Jézéquel. Finally, the ECMFA committees are acknowledged.