A critical gap in existing literature is the lack of detailed knowledge about the experience of hospitals undergoing the process of collaboration. A primary purpose of this study is to close this gap by gaining a deeper understanding of a hospital’s experience living through such a change—i.e., perceptions about key issues, concerns, and performance differences during implementation. Two primary research questions were explored: (1) How do health care organizations undergoing collaboration manage the change process? (2) What are the key success factors for collaboration? This research compared the processes of two very different collaborative efforts: the merger of the Beth Israel Hospital and the New England Deaconess Medical Centers into the Beth Israel Deaconess Medical Center (BIDMC) and the alliance of the Brigham and Women’s Hospital and the Massachusetts General Hospital into Partners HealthCare System (PHCS).