This article presents an explorative study of the impact of Communities of Practice (CoPs) on the success of a certain category of Knowledge Management Systems, hereafter called Expert Recommender Information Systems. They regroup Information Systems that identify and display individuals who have been qualified by the system as experts, and who are in a position to help users solve problems involving a business process breakdown. Rather than focusing on the Expert Recommending Information System itself, the author concentrates on the service it delivers, the Expert Recommending Service (ERS). Using multiple case study research, five different organizations were investigated, essentially in order to identify how CoPs influence the success of their ERS.