摘要:Background: Community-based outreach seeks to move libraries beyond their traditional institutional boundaries to improve both access to and effectiveness of health information. The evaluation of such outreach needs to involve the community in assessing the program's process and outcomes. Purpose: Evaluation of community-based library outreach programs benefits from a participatory approach. To explain this premise of the paper, three components of evaluation theory are paired with relevant participatory strategies. Concepts: The first component of evaluation theory is also a standard of program evaluation: use. Evaluation is intended to be useful for stakeholders to make decisions. A useful evaluation is credible, timely, and of adequate scope. Participatory approaches to increase use of evaluation findings include engaging end users early in planning the program itself and in deciding on the outcomes of the evaluation. A second component of evaluation theory seeks to understand what is being evaluated, such as specific aspects of outreach programs. A transparent understanding of the ways outreach achieves intended goals, its activities and linkages, and the context in which it operates precedes any attempt to measure it. Participatory approaches to evaluating outreach include having end users, such as health practitioners in other community-based organizations, identify what components of the outreach program are most important to their work. A third component of evaluation theory is concerned with the process by which value is placed on outreach. What will count as outreach success or failure? Who decides? Participatory approaches to valuing include assuring end-user representation in the formulation of evaluation questions and in the interpretation of evaluation results. Conclusions: The evaluation of community-based outreach is a complex process that is not made easier by a participatory approach. Nevertheless, a participatory approach is more likely to make the evaluation findings useful, ensure that program knowledge is shared, and make outreach valuing transparent.