This is the third brief in a series: "Building a Post-Care Service System in Child Welfare: Lessons Learned from the Frontlines of Implementation Science in Catawba County." The first of the three briefs provided background information on the initiative that is the focus of the series--the Catawba County Child Wellbeing Project. Both Brief 2 and this third brief examine the Project's use of implementation science--scientific methods that promote the uptake of research into routine practice settings--to help bring about systems change. While one of the co-authors of Brief 2 is a staff member of the Catawba County (North Carolina) Department of Social Services, which operates the project, that brief mainly discusses the Project's use of implementation science from the perspective of its technical assistance providers. In contrast, this brief discusses lessons learned from using implementation science in the Project from the perspective of the Catawba County Department. The lessons discussed in this brief fall into six areas: 1) using a ground-up process to plan the Project, 2) building the team infrastructure, 3) vetting and selecting interventions to use in the Project, 4) building agency infrastructure to support those interventions, 5) working with program developers, and 6) continuous program improvement efforts. [For related briefs, see "Using Implementation Science to Support and Align Practice and System Change: A Case Study of the Catawba County Child Wellbeing Project. Research-to-Results Brief. Publication #2012-17" (ED534865) and "Implementing a Post-Care Service System in Child Welfare: The Catawba County Child Wellbeing Project. Research-to-Results Brief. Publication #2012-16" (ED534864).]