This paper describes and discusses the development of an operational expert system for routine use in industry for the selection of industrial adhesives. Inter alia, it discusses the logical complexity of the problem (which is greater than is intuitively apparent), the problems of knowledge-acquisition (including experiments in inductively deriving rules from examples). It includes a review of the desired characteristics of a tool for developing such a system (including, rules, frames and class objects). Unlike many systems reported in the literature, this system can be evaluated according to pre-existing criteria. On such an evaluation it is shown to produce very large gains in productivity. A separate paper will describe and discuss the structure of the system.