The Office of Juvenile Justice and Delinquency Prevention's (OJJDP) Model Programs Guide (MPG) contains information about evidence-based juvenile justice and youth prevention, intervention, and reentry programs. The MPG is a resource for practitioners and communities about what works, what is promising, and what does not work in juvenile justice, delinquency prevention, and child protection and safety. This document provides a summary of background information gathered to inform the development of Implementation Guides for OJJDP's MPG. It synthesizes and analyzes the existing research on implementation science with information collected through the course of qualitative focus groups, interviews, and internal discussions to highlight the themes that emerged about implementing evidence-based programs.