This book constitutes the refereed proceedings of the 20th International Conference on Runtime Verification, RV 2020, held in Los Angeles, CA, USA, in October 2020. The conference was held virtually due to the COVID-19 pandemic. The 14 regular papers and 2 short papers presented in this book were carefully reviewed and selected from 43 submissions. Also included are an invited paper, 5 tutorial papers, 6 tool papers, and a benchmark paper. The RV conference is concerned with all aspects of monitoring and analysis of hardware, software and more general system executions. The papers are organized in the following topical sections: runtime verification for autonomy; runtime verification for software; runtime verification with temporal logic specifications; stream-based monitoring; and runtime verification for cyber-physical systems.