This computer science textbook offers an introduction to the theory and practice of formal specification, defined as the use of discrete mathematics for describing the function of hardware and software systems. Formal specification plays a vital role, especially with regard to problem-free installation. Designed for students approaching the subject for the first time, this text develops all the required analytical and mathematical techniques. Numerous worked examples and exercises demonstrate actual software and computer systems. The book culminates with an introduction to "Z", a formal notation which is particularly useful for unambiguously specifying systems.