parallel replica dynamics was proposed by a.f. voter as a tool for accelerating molecular dynamics simulations characterized by a sequence of infrequent, but rapid, transitions from one state to another. an example would be the migration of a defect through a crystal. parallel replica dynamics accelerates this by simulating many replicas simultaneously, concatenating the simulation times of the realizations as though it were a single long trajectory. this motivates important questions: is parallel replica dynamics algorithm doing what we hope? for what systems will it be useful? how do we implement it efficiently? in this talk, i will thoroughly describe the algorithm and report on progress towards rigorous justification. open questions and related problems will also be discussed.