This is a textbook for final year undergraduates/first year graduates in computer science, as well as a useful introduction for research students seeking a solid introduction to more specialist literature. This text emphasises the role of calculus in programming language design and implementation, denotational semantics, and domain theory. Alternative books on the subject have been written by logicians, but this is the first to have been written from a computer science prespective, invaluable in emphasising the practical relevance of the key theortical ideas.