The need for further research into purchase decision making in industrial markets is widely acknowledged. Tor marketing techniques to be effective, the decision makers must be identified and their roles and the criteria they use understood. But in practice marketing decisions are often based on certain generalised assumptions about the purchasing process. The paper briefly discusses the main conclusions of such studies and their implications for marketing and communications. After discussing the difficulties inherent in any investigation of purchase decision-making, the "case history" approach to the task is then described: this is essentially an attempt to gain a qualitative understanding of vision-making in a particular market by exhaustive investigations of a small sample of specific purchasing instances. An account of one such case history study is then given: the marketing considerations which lead to the study are summarised, and the course of the study and the principles on which it proceeded are described. The findings of the study and their relevance to marketing and advertising planning are then outlined. Finally the methodological problems encountered and the inherent limitations of the case history approach are discussed.