This paper assesses the state-of-the-art research on CRM integration. Firstly, we discuss some basics of CRM integration and its importance for corporate performance on the project or enterprise level. Afterwards we give attention to reasons for CRM projects' failures. We show that integration is a complex term that lacks a common definition and is differently perceived by authors from different domains. Only few authors focus on the comprehensive integration of CRM within a company setting. The discussion is monopolized by the specific domain from which the authors come. Interestingly, applicable theories of the firm are not widely employed as a foundation from which to explain CRM integration. In conclusion we propose a CRM integration model which offers a combination and consolidation of our research results as well as a foundation for a theory-based and empirical assessment of CRM integration issues.