This book constitutes the refereed proceedings of the 6th International Workshop on Reachability Problems, RP 2012, held in Bordeaux, France, in September, 2012. The 8 revised full papers presented together with 4 invited talks were carefully reviewed and selected from 15 submissions. The papers present current research and original contributions related to reachability problems in different computational models and systems such as algebraic structures, computational models, hybrid systems, logic and verification. Reachability is a fundamental problem that appears in several different contexts: finite and infinite-state concurrent systems, computational models like cellular automata and Petri nets, decision procedures for classical, modal and temporal logic, program analysis, discrete and continuous systems, time critical systems, and open systems modeled as games.