This book constitutes the proceedings of the 13th International Symposium on NASA Formal Methods, NFM 2021, held virtually in May 2021.The 21 full and 3 short papers presented in this volume were carefully reviewed and selected from 66 submissions. The papers aim to identify challenges and provide solutions to achieve assurance in mission-critical and safety-critical systems. Examples of such systems include advanced separation assurance algorithms for aircraft, next-generation air transportation, autonomous rendezvous and docking of spacecraft, on-board software for unmanned aerial systems (UAS), UAS traffic management, autonomous robots, and systems for fault detection, diagnosis, and prognostics.

This book constitutes the proceedings of the 10th International Symposium on NASA Formal Methods, NFM 2018, held in Newport News, VA, USA, in April 2018. The 24 full and 7 short papers presented in this volume were carefully reviewed and selected from 92 submissions. The papers focus on formal techniques and other approaches for software assurance, their theory, current capabilities and limitations, as well as their potential application to aerospace, robotics, and other NASA-relevant safety-critical systems during all stages of the software life-cycle.