First published in 1990, this book discusses the application of formal methods to the human-computer interface. Formal methods - the attempt to provide methods that rigourously and unambiguously describe the behaviour of a computer program or system - is receiving a great deal of attention in human-computer interaction (HCI). Topics such as the specification of a system, the construction of a system from its specification and the abstraction of a specification from an existing system, are clearly of great theoretical and practical interest. The contributors to the work are well-known in the field of HCI and their articles cover much of the work in the area. The book is a series of papers specially commissioned by the editors for the book; it is thus a coherent and important contribution to the area.