Evaluating civil society organizations remains a pressing issue in the sector. Civil society leaders today face a dizzying array of models and approaches but evaluating the outcomes and impacts of these organizations remains challenging. Many of the changes civil society organizations (CSOs) pursue take a long time to address and are difficult to measure. Engaging in an evaluation requires making key decisions about the criteria, standards, and evidence that will be used to judge the merit or worth of the program, organization, or network. With multiple stakeholders, each with their own ideas about what may constitute successful change, determining who makes these decisions affects what gets measured, which affects how CSOs do their work. Despite these challenges, scholars and practitioners continue to work to develop more applicable and innovative approaches to assessing the contributions of civil society organizations. After giving a brief introduction and historical background to evaluation, this essay looks at some key issues in evaluating civil society organizations and concludes with recent developments on this important topic.