Fixed point calculus is about the solution of recursive equations de˛ned by a monotonic endofunction on a partially ordered set. This tutorial presents the basic theory of ˛xed point calculus together with a number of applications of direct relevance to the construction of computer programs. The tutorial also presents the theory and application of Galois connections between partially ordered sets. In particular, the intimate relation between Galois connections and ˛xed point equations is amply demonstrated. ∗ School of Computer Science and Information Technology, University of Nottingham, Nottingham NG8 1BB, England 1