While work on maritime autonomous surface ships (MASS) regulation has commenced, regulation of autonomous navigational systems—the primary future driver of ship safety performance—remains unexplored. This paper seeks to address this gap. The chapter analyzes MASS as technological artefacts. In addition, the chapter assesses the utility and future of rules-based and performance-based instruments for MASS navigational safety regulation. To this end, the chapter argues that as MASS navigational systems are complex cyber-physical data processing assemblages containing both hardware, traditional software and machine learning software components, future regulatory frameworks will likely converge a layered regulatory design. The design will consist of performance standards verified by simulation MASS navigation, buttressed by performance real-world testing environment and online tests and limited rules-based technical standards. Autonomous navigation subsystems (ANS) technological complexity and machine learning software components will likely entail that only comprehensive simulation-based testing allows regulators to explore navigational edge cases in sufficient detail to ensure safe operation. However, the simulation-based tests will be buttressed by real-world testing both in trial areas and in real traffic. Crucial questions over required safety levels, testing environment parameter specifications, and operating responsibilities remain open. Further research and regulatory drafting work should concentrate on these areas.