Thisbook constitutes the refereed proceedings of the 9th InternationalWorkshop on Reachability Problems, RP 2015, held in Warsaw, Poland, in September 2015. The 14 papers presented together with 6 extended abstracts in this volume were carefully reviewed and selected from 23 submissions. The papers cover a range of topics inthe field of reachability for infinite state systems; rewriting systems;reachability analysis in counter/timed/cellular/communicating automata;Petri nets; computational aspects of semigroups, groups, and rings; reachability in dynamical and hybrid systems;frontiers between decidable and undecidable reachability problems; complexity and decidability aspects; predictability in iterative maps and new computational paradigms.
