This book constitutes the refereed proceedings of the 9th International Workshop 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 in the 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;...