This book constitutes the thoroughly refereed post-proceedings of the Third International Workshop on SDL and MSC, SAM 2002, held in Aberystwyth, UK in June 2002. The 15 revised full papers presented were carefully selected during two rounds of reviewing and revision. A broad variety of current issues on SDL and on MSC and TTCN are addressed, in particular languages for collaborative specification, visual requirements description, constraints in SDL, SDL extensions, protocol design, UMS protocol implementation, use case map scenarios, message sequence charts, MSC connectors, MSC-2000 extensions, and TTCN-3 in relation to UML and MSC.