This qualitative study examined foster parents' perceptions of the initial transition period in order to better understand the family formation process that occurs when a new placement is transitioned into the home. A snowball sampling method was used to recruit ten foster parents to participate. A constant comparative analysis of interview transcripts guided by grounded theory approaches yielded a model of the foster family transition process that identified three main tasks: establishing trust and a sense of belonging; re-establishing family homeostasis; and working with external stakeholders. Responsive, trauma-sensitive care; realistic expectations; parenting skills; and access to resources facilitated foster family movement through the transition process. While foster families shared many of the same tasks as other family forms adding a new member, unique aspects of the foster family context were identified. Foster families often form with an incomplete knowledge of the new family member's medical and trauma history and under the oversight of the social service system. Unlike other family types, permanence is not the primary objective of foster family formation. Study findings have implications for foster parent training and support during the transition of a new placement and affirm the value of including foster parents' perspectives in research.