AbstractFor a variety of reasons, the finding of an optimal solution is impractical for many O.R. problems. A common way of overcoming this unhappy state of affairs is the development of heuristic (approximate) methods. The purpose of this paper is to discuss some of the issues that arise with such an approach-that is, the use of a method which, on the basis of experience of judgement, seems likely to yield good solutions but which cannot guarantee optimality. The use of such methods is motivated by the emergence of the theory ofNP-completeness, i.e. the study of the complexity of algorithms, which is briefly introduced. A number of heuristic methods are presented in order to illustrate some of the ideas discussed. Heuristic procedures are classified according to design. Some of the problems of both how to design effective heuristics and how to use heuristics in the real world are discussed.