The transition of service is the most critical phase of in- or outsourcing. Ultimately, the transition must be to ensure a gradual transition to a successful collaboration between business, demand supply organization and service provider. A transition requires the explicit holding of the responsibilities, and the proper transfer of staff and related resources from the contracting organization to the service provider. Based on the Sourcing Phase Model© and the Five Aspect Model©, Quint has developed an approach that enables organizations to control the transition well and increase the maturity of the service provisioning. Quint’s sourcing consultants have managed several transitions, and understand the key elements of a successful transition.