This paper addresses the concept of "implementation outcomes" in implementation research, distinguishing them from service system and clinical treatment outcomes. It proposes a working taxonomy of eight conceptually distinct implementation outcomes: acceptability, adoption, appropriateness, feasibility, fidelity, implementation cost, penetration, and sustainability. These outcomes are defined and discussed, with their theoretical basis, measurement approaches, and relevance to implementation processes. The paper outlines a two-pronged research agenda: (1) conceptualizing and measuring implementation outcomes to enhance understanding of implementation processes and improve efficiency in implementation research; and (2) building theory to inform the development and evaluation of implementation strategies. The paper emphasizes the importance of conceptual clarity and consistent terminology in implementation research, as well as the need for empirical studies to validate and refine definitions of implementation outcomes. It also highlights the interrelationships among implementation outcomes and their role in determining the success of implementation efforts. The paper calls for further research to explore these outcomes in various contexts and to develop measures that can be used to evaluate the effectiveness of implementation strategies. The proposed taxonomy aims to advance the language and conceptualization of implementation outcomes in the field of implementation science.This paper addresses the concept of "implementation outcomes" in implementation research, distinguishing them from service system and clinical treatment outcomes. It proposes a working taxonomy of eight conceptually distinct implementation outcomes: acceptability, adoption, appropriateness, feasibility, fidelity, implementation cost, penetration, and sustainability. These outcomes are defined and discussed, with their theoretical basis, measurement approaches, and relevance to implementation processes. The paper outlines a two-pronged research agenda: (1) conceptualizing and measuring implementation outcomes to enhance understanding of implementation processes and improve efficiency in implementation research; and (2) building theory to inform the development and evaluation of implementation strategies. The paper emphasizes the importance of conceptual clarity and consistent terminology in implementation research, as well as the need for empirical studies to validate and refine definitions of implementation outcomes. It also highlights the interrelationships among implementation outcomes and their role in determining the success of implementation efforts. The paper calls for further research to explore these outcomes in various contexts and to develop measures that can be used to evaluate the effectiveness of implementation strategies. The proposed taxonomy aims to advance the language and conceptualization of implementation outcomes in the field of implementation science.