Over the last years, IT outsourcing customers have shifted their focus to multi-sourcing. To cope with the ever-increasing complexity of their multi-provider portfolios, companies aim to develop and hone their service integration capabilities. They adapt their IT organizations to enable more efficient and effective service management for their broad service landscapes. Nowadays, most IT service management implementations build on best practice of the IT Infrastructure Library (ITIL). ITIL, however, does neither reflect multi-tenant sourcing models nor end-to-end service integration. IT service management needs to evolve to meet the new requirements of service integration. So far, however, there is a lack of guidance on how to adequately adapt IT service management for integration of multiple sourcing arrangements. Our research contributes to both theory and practice by developing a ranking of IT service management processes according to their importance for service integration success. For three important processes, we then reveal adequate implementations and process designs derived from real-life scenarios. Our results are developed during an multi-stage research study, incorporating insights from expert interviews, a quantitative questionnaire study, and case study research. The insights gained should enable multi-sourcing customers to build more successful service integration solutions, as well as academics to shape future research in this area.