Foster homes are a critical resource within the child welfare system, with more than 260,000 children in non-relative foster care at the end of FY2001. Child welfare agencies are continually challenged to provide adequate numbers of foster homes that are stable, can accommodate sibling groups, and are located in proximity to family members. Research on foster parent retention is surprisingly slender, however, with little known about the length of time served by foster parents and the characteristics associated with varying length of service. This study was designed to extend current understanding of foster parent retention by producing unbiased estimates of length of service and examining factors associated with licensure, provision of care, and length of service. The study used administrative data, applying data management and analytical methods that have previously been used by researchers to describe the length of stay for children in foster care. Principal research questions include: How have the characteristics of foster parents changed over time? How can variations in activity levels be described, and what foster parent characteristics are associated with varying activity levels? What is the typical length of service for foster parents? What characteristics are associated with variations in length of foster parent careers?