This book constitutes the proceedings of the 12th International Symposium on NASA Formal Methods, NFM 2020, held in Moffett Field, CA, USA, in May 2020.*

The 20 full and 5 short papers presented in this volume were carefully reviewed and selected from 62 submissions. The papers are organized in the following topical sections:  learning and formal synthesis; formal methods for DNNs; high assurance systems; requirement specification and testing; validation and solvers; solvers and program analysis; verification and times systems; autonomy and other applications; and hybrid and cyber-physical systems.