In this article, the authors describe the development, psychometric characteristics, and potential utility of the "Wraparound Fidelity Index" (WFI), a multi-informant measure designed to assess providers' adherence during service delivery to the essential elements of wraparound. Results from 408 families across 16 sites in nine states indicated adequate psychometrics for use of the WFI as an overall fidelity measure. The psychometrics for individual element scores were less reliable, however. The authors discuss the implications for research and practice, identifying specific items to be revised and potential uses for the WFI. They also cover policy implications, including how to overcome challenges observed in implementing the wraparound approach nationally.