Central to Formal Methods is the so-called Correctness Theorem which relates a specification to its correct Implementations. This theorem is the goal of traditional program testing and, more recently, of program verification (in which the theorem must be proved). Proofs are difficult, though even with the use of powerful theorem provers. This volume explains and illustrates an alternative method, which allows the construction of (necessarily correct) algorithms from a specification using algebraic transformations and refinement techniques which prevent the introduction of errors. Based on teaching material used extensively at Loughborough University, John Cooke introduces the basics, using simple examples and lots of detailed working (which can often be re-used). Predicate calculus is used in preference to a specific specification language, the contents being equally applicable to languages such as VDM_SL and Z. Constructing Correct Software will provide invaluable reading for students and practitioners of Computer Science and Software Engineering to whom correctness of software is of prime importance. The new edition contains the following additions and improvements: 1 The concept of 'eureka' steps. These allow the introduction of a computational process by means of a recursive function defined implicitly by a set of 'reducing' transformation rules. 2 Explicit explanation of the links between testing, verification and construction. Also more links between comments, assertions and correctness, and 'structured programming'. 3 A web-based appendix to support the further examples and transformations in the text. There is now more interest in the States and Britain in formal methods, which is probably a product of more highly-trained programmers being at a premium in the wake of the explosion and then drying-up of employment opportunities in IT.