An electronic marketplace supports the interaction among different users to exchange information about products to sell and buy. Significance of electronic marketplaces is given by the huge amount of web sites that are currently available providing services in almost any area one can think of. However, existing similarities among these sites are not precisely documented which strongly restrains software reuse during the development of new electronic marketplaces. To improve this situation, we propose an analysis pattern that describes both the structural and the behavioural properties of a generic electronic marketplace. Then, developing a new electronic marketplace will correspond just to provide a particular adaptation of our pattern. In this way, reuse of our pattern contributes to reducing the costs of the development of new electronic marketplaces.