The LARCH family of formal specification languages and tools was originally developed in the USA. Its user community has now spread to Europe and several industrial trial firms are interested in using it in their system development programs. It differs from the other higher profile file languages such as Z and VDM in three respects: firstly, it was designed to specify programs rather than mathematical models and therefore addresses the complexities of real programs; secondly, it has been specifically developed as a practical tool for use in several major application domains; finally, it has a state-of-the-art semantic analysis tool in the form of the LARCH Prover. This volume contains the papers presented at the First International Workshop on LARCH, held in Dedham, USA, 13-15 July 1992. The workshop brought together for the first time those who have designed the LARCH languages, built tool support for them, and used them to specify and reason about soft- and hardware systems. It encouraged discussion about how the LARCH languages and Prover are being used, and assessed plans for development oping them. The aim of the workshop was to raise the profile of LARCH, and to provide impetus for continued research into its tools and languages. Among the topics covered in this volume are: the mechanical verification of concurrent systems with TLA; the DECspec project; the preliminary design of LARCH/C++; generating proof obligations for circuits; lock-level verification; checking software design using formal specifications; optimising programs with specifications; and a report on the formal basis of generics. First International Workshop on LARCH provides a comprehensive overview of the international use and development of LARCH. It should be useful to researchers and practitioners who are already involved with, or who wish to know more about, this important specification language.