ABSTRACT. Citizens have long contributed to scientific research about the environment through volunteer environmental monitoring programs. Their participation has also resulted in outcomes for themselves, their communities, and the environment. This research synthesizes 35 peer-reviewed journal articles that reported such outcomes through 2012. This collection of articles was derived from a pool of 436 peer-reviewed journal articles about participatory environmental monitoring. Reported outcomes for participants and communities ranged from increasing personal knowledge and community awareness to changing attitudes and behaviors, building social capital, and ultimately, influencing change in natural resource management and policies. Mixed results were reported in regard to citizen participation in natural resource decision-making processes and in terms of participant knowledge gain. Future research recommendations that address identified knowledge gaps include the following: (1) assessing knowledge beyond the basic content of the subject of monitoring to better address the value of volunteer environmental monitoring as a public participation tool; (2) conducting independent research across programs to enable null or negative outcome reporting, understand commonalities of outcomes across programs, and make linkages between outcomes and program characteristics; (3) carrying out rigorous research that includes data collection and statistical analysis focused on the effectiveness of citizen participation in decision making; (4) assessing the time component of outcome achievement to inform the volunteer monitoring community; and (5) conducting additional research to identify changes in attitudes and behaviors, particularly geared toward minimizing losses in biodiversity and impacts of climate change.