AIMS: Stakeholder engagement is fundamental to comparative effectiveness research (CER), but lacks consistent terminology. This paper aims to define stakeholder engagement and present a conceptual model for involving stakeholders in CER. MATERIALS #ENTITYSTARTX00026; METHODS: The definitions and model were developed from a literature search, expert input and experience with the Center for Comparative Effectiveness Research in Cancer Genomics, a proof-of-concept platform for stakeholder involvement in priority setting and CER study design. RESULTS: Definitions for stakeholder and stakeholder engagement reflect the target constituencies and their role in CER. The 'analytic-deliberative' conceptual model for stakeholder engagement illustrates the inputs, methods and outputs relevant to CER. The model differentiates methods at each stage of the project; depicts the relationship between components; and identifies outcome measures for evaluation of the process. CONCLUSION: While the definitions and model require testing before being broadly adopted, they are an important foundational step and will be useful for investigators, funders and stakeholder groups interested in contributing to CER.