Formal specification is a method for precisely modelling computer-based systems that combines concepts from software engineering and mathematical logic. In this book the authors describe algebraic and state-based specification techniques from the unified view of the Common Object-oriented Language for Design, COLD, a wide-spectrum language in the tradition of VDM and Z. The kernel language is explained in detail, with many examples, including: set representation, a display device, an INGRES-like database system, and a line editor. Fundamental techniques such as initial algebra semantics, loose semantics, partial functions, hiding, sharing, predicate and dynamic logic, abstraction functions, representation of invariants and black-box correctness are also presented. More advanced ideas, for example Horn logic, and large systems are given in the final part. Appendices contain full details of the language's syntax and a specification library. Techniques for software development and design are emphasised throughout, so the book will be an excellent choice for courses in these areas.