Systems collaboration has repeatedly been cited as a component of successful social service delivery. Through qualitative data, this study explored the process involved in inter-agency collaboration when providing Integrative Family and Systems Treatment (I-FAST) for families with severely emotionally or behaviorally disturbed children. Data were collected through a series of eight focus groups with 26 agency collaborators across 11 counties in Ohio. Data analysis revealed two emergent phenomena: the process of developing collaboration, consisting of making initial contact, a trial period and developing trust; and the key ingredients of collaboration, focusing on interpersonal and professional qualities. Implications of each theme are discussed.