The HOL system is a higher order logic theorem proving system implemented at Edinburgh University, Cambridge University and INRIA. Its many applications, from the verification of hardware designs at all levels to the verification of programs and communication protocols are considered in depth in this volume. Other systems based on higher order logic, namely Nuprl and LAMBDA are also discussed. Features given particular consideration are: novel developments in higher order logic and its implementations in HOL; formal design and verification methodologies for hardware and software; public domain availability of the HOL system. Papers addressing these issues have been divided as follows: Mathematical Logic; Induction; General Modelling and Proofs; Formalizing and Modelling of Automata; Program Verification; Hardware Description Language Semantics; Hardware Verification Methodologies; Simulation in Higher Order Logic; Extended Uses of Higher Order Logic. Academic and industrial researchers involved in formal hardware and software design and verification methods should find the publication especially interesting and it is hoped it will also provide a useful reference tool for those working at software institutes and within the electronics industries.