It is with great pleasure that we present to you this tutorial volume entitled Validation of Stochastic Systems.ItisoneoftheresultsoftheDutch-German- lateral cooperation project "Validation of Stochastic Systems" (VOSS), ?nanced by NWO and DFG (the Dutch and German science foundations, respectively). In the early days of 2002, the idea emerged to organize a seminar at Schloss Dagstuhl, not the usual Dagstuhl seminar with primarily invited participants, but a seminar aimed at young(er) people, and for which the organizers assign themes to be worked upon and presented on. Following an open call announced via the Internet in the spring of 2002, we received many applications for part- ipation. After a selection procedure, we decided to assign (mostly) teams of two researchers to work on speci?c topics, roughly divided into the following four theme areas: "Modelling of Stochastic Systems," "Model Checking of Stochastic Systems," "Representing Large State Spaces," and "Deductive Veri?cation of Stochastic Systems." These are the titles of the four parts of this volume. TheseminarwasheldinSchlossDagstuhlduringDecember8-11,2002aspart of the so-called GI/Research Seminar series. This series of seminars is ?nancially supported by theGesellschaft fur ] Informatik, the German Computer Society. At that point in time the papers had already undergone a ?rst review round. Each of the tutorial papers was presented in a one-hour session, and on the basis of the presentations we decided to bring together a selection of them into a book.