This paper addresses the unresolved issue in implementation research of how to conceptualize and evaluate successful implementation. It introduces the concept of "implementation outcomes," distinct from service system and clinical treatment outcomes, and proposes a heuristic taxonomy of eight conceptually distinct implementation outcomes: acceptability, adoption, appropriateness, feasibility, fidelity, implementation cost, penetration, and sustainability. Each outcome is defined with a nominal definition and a level of analysis. The paper also outlines a two-pronged research agenda for advancing the understanding of implementation outcomes, focusing on conceptualization and measurement, and theory building. The authors emphasize the importance of consistent terminology, referent for rating outcomes, level of analysis, construct validity, measurement properties, and the salience of outcomes to stakeholders and at different points in the implementation process. They suggest that reliable and valid measures of implementation outcomes will enable empirical testing of implementation success and comparative effectiveness research on implementation strategies.This paper addresses the unresolved issue in implementation research of how to conceptualize and evaluate successful implementation. It introduces the concept of "implementation outcomes," distinct from service system and clinical treatment outcomes, and proposes a heuristic taxonomy of eight conceptually distinct implementation outcomes: acceptability, adoption, appropriateness, feasibility, fidelity, implementation cost, penetration, and sustainability. Each outcome is defined with a nominal definition and a level of analysis. The paper also outlines a two-pronged research agenda for advancing the understanding of implementation outcomes, focusing on conceptualization and measurement, and theory building. The authors emphasize the importance of consistent terminology, referent for rating outcomes, level of analysis, construct validity, measurement properties, and the salience of outcomes to stakeholders and at different points in the implementation process. They suggest that reliable and valid measures of implementation outcomes will enable empirical testing of implementation success and comparative effectiveness research on implementation strategies.