To understand the impact of an enterprise system on a company’s business, an approach is proposed in which the company’s business relationships are seen as a valuable resource that needs to be managed. Extensive studies of mainly industrial companies’ business with each other carried out by researchers belonging to the IMP Group (see www.impgroup.org) have shown that the companies have a limited number of long-term business relationships with what are considered important customers and suppliers (Ford, Gadde, Håkansson, & Snehota, 2003; Håkansson & Snehota, 1995). These business relationships often involve several people with different business functions, given that the exchanged product or service might be complex and that it is often adapted to the customer’s requirements. This matching process between a buyer and a seller is sometimes discussed in terms of homogeneous markets (Alderson, 1965; Penrose, 1959) where the exchanged value needs to be scrutinized and negotiated by the partners involved. Thus, prior to a business exchange of the product and service for a negotiated price, there will be information exchanges as well as personal interactions between different employees from both the selling and buying companies. This chapter addresses the research question of how do enterprise systems support the business activities that take place in a business relationship? An underlying assumption is that the enterprise system can help the participating staff by supporting the execution of their business activities. The following chapter presents lessons from case studies of two large companies’ business relationships with customer and partner companies. The aim of the chapter is to offer an insight in how enterprise systems are used in an interorganizational setting, with an emphasis on marketers and salesmen. It also shows the challenges that companies aiming for a fully integrated enterprise system are facing.