Abstract-The successful deployment of many autonomous systems in part hinges on providing rigorous guarantees on their performance and safety through a formal verification method, such as reachability analysis. In this work, we present a simple-to-implement, sampling-based algorithm for reachability analysis that is provably optimal up to any desired approximation accuracy. Our method achieves computational efficiency by judiciously sampling a finite subset of the state space and generating an approximate reachable set by conducting reachability analysis on this finite set of states. We prove that the reachable set generated by our algorithm approximates the ground-truth reachable set for any user-specified approximation accuracy. As a corollary to our main method, we introduce an asymptoticallyoptimal, anytime algorithm for reachability analysis. We present simulation results that reaffirm the theoretical properties of our algorithm and demonstrate its effectiveness in real-world inspired scenarios.I. INTRODUCTION Autonomous and highly automated systems inherently depend on effectively incorporating rigorous guarantees on the performance and safety through formal verification and validation methods. For instance, in order to ensure collision-free paths, advanced driver-assistance systems need to be capable of anticipating all potential actions of the driver without overly conservative assumptions. This requires performing on-line reachability analysis, i.e., computation of states that these vehicles can reach within a given time interval. It can also serve as a supervisory mechanism for any motion planner that incorporates deep learning. Going beyond the realm of autonomous driving, reachability analysis has shown promise as a tool for formal verification of a wide variety of systems. Applications of reachability analysis include safety, correctness, and controller synthesis problems involving intricate specifications or robotic systems such as autonomous aircraft and cars, medical robots, and personal-assistance robots.Typically the state of a system is not fully observable, e.g., a car might not have precise knowledge about its position. Thus, conducting accurate reachability analysis by definition requires reasoning about all possible trajectories from every possible state. Reasoning about all possible behaviors of a system renders reachability analysis computationally intractable in practice [3]. This computational challenge is further compounded by the generally large size and high complexity of the system in consideration, and the practical need to obtain verification results in a reasonably short time (i.e., seconds or minutes, not days) for the sake of, for example,