Information systems are integrated in the daily business of companies, to support the exchanges with its counterparts. To manage these information systems, companies often turn to third parties: information system providers (IS-providers). IS-providers have competences that the companies become dependent on and they are therefore important for maintaining the company’s business performance. The companies develop dependencies on their information systems and thereby also on their IS-providers. This thesis studies the connection between a company’s relationships with IS-providers and its other business relationships. A single case study of how a focal company’s IS-providers impact the company’s customer relationships is conducted. The applied analytical framework combines an information system’s perspective and a business relationship perspective. The analytical level is guided by the concept of connection, which has its origin in the business relationship perspective. The information system’s perspective illustrates the characteristics of the information systems that the IS-providers manage. The business relationship perspective studies each business relationship as unique, originating in different exchanges and behaviour. The single case study involves five customer relationships and four IS-provider relationships, creating twenty within-cases. The results show that IS-providers impact differently on the business relationships of companies. The impact on companies is contingent on the information exchanges with the IS-providers, which integrate the information systems in their customer business relationships. The impact is explained by the strength of the connection and the degree of continuity of the connection. The strength of the connection depends on how the information system is used and which of the IS-providers are connected. The impact from one IS-provider can be described as a homogenous impact on all the connected business relationships. However, different IS-providers have different types of impacts, meaning that when a company has several IS-providers, the impact is heterogeneous. The study shows that the impact is most commonly positive. The thesis is of interest for researchers who wish to understand the interconnectedness between business relationships, and of value for business professionals, who wish to increase their understanding of the complex situation of using IS-providers for management of their information systems and the impact they have on their other business relationships.