This book constitutes the proceedings of the 20th IFIP International Conference on Distributed Applications and Interoperable Systems, DAIS 2020, which was supposed to be held in Valletta, Malta, in June 2020, as part of the 15th International Federated Conference on Distributed Computing Techniques, DisCoTec 2020. The conference was held virtually due to the COVID-19 pandemic. The 10 full papers presented together with 1 short paper and 1 invited paper were carefully reviewed and selected from 17 submissions. The papers addressed challenges in multiple application areas, such as privacy and security, cloud and systems, fault-tolerance and reproducibility, machine learning for systems, and distributed algorithms.