The large gap between intervention outcomes demonstrated in efficacy trials and the apparent ineffectiveness of these same programs in community settings has prompted investigators and practitioners to look closely at implementation fidelity. Critically important, but often overlooked, are the implementers who deliver evidence-based programs -- the effectiveness of programs cannot surpass skill levels of the people implementing them. This article distinguishes fidelity at the programmatic level from implementer fidelity. Two components of implementer fidelity are defined. Implementer adherence and competence are proposed to be related but unique constructs that can be reliably measured for training¸ monitoring, and outcomes research. Observational measures from a school-based preventive intervention are provided and the unique contributions of implementer adherence and competence are illustrated. Distinguishing implementer adherence to the manual and competence in program delivery is a critical next step in child mental health program implementation research.