This study examined the role of inter-organizational collaboration in implementing new evidence-based practices for addressing problem behaviors in at-risk youth. Semi-structured interviews were conducted with 38 systems leaders of probation, mental health, and child welfare departments of 12 California counties participating in a large randomized controlled trial to scale-up the use of Multidimensional Treatment Foster Care. Three sets of collaboration characteristics were identified: (1) characteristics of collaboration process, (2) characteristics of the external environment, and (3) characteristics of participating organizations and individuals. Inter-organizational collaboration enables an exchange of information and advice and a pooling of resources individual agencies may require for successful implementation.