Issues in V&V of autonomous and adaptive systems

System autonomy is attracting increasing attention in many application domains, yet complete understanding of autonomous and adaptive (A&A) systems and their verification and validation (V&V) remain a challenge. In recent years, formal methods have been effectively used in V&V of safety/mission-critical systems. The paper provides an overview of different formal techniques being used in reasoning about system autonomy and challenges they currently encounter. We also highlight some of the active research issues in V&V of autonomous and adaptive systems.