The following technical report is available from http://aib.informatik.rwth-aachen.de: Replaying Play in and Play out: Synthesis of Design Models from Scenarios by Learning Benedikt Bollig, Joost-Pieter Katoen, Carsten Kern, Martin Leucker AIB 2006-12 This paper is concerned with bridging the gap between requirements, provided as a set of scenarios, and conforming design models. The novel aspect of our approach is to exploit learning for the synthesis of design models. In particular, we present a procedure that infers a message-passing automaton (MPA) from a given set of positive and negative scenarios of the system's behavior provided as message sequence charts (MSCs). The paper investigates which classes of regular MSC languages and corresponding MPAs can (not) be learned, and presents a dedicated tool based on the learning library LearnLib that supports our approach.