Context: Collective gardens are increasingly considered a tool to promote health and well-being. Objective: In this systematic review, we critically appraise quantitative studies exploring the potential health benefits of urban collective garden participation. Data Sources: Articles published between January 2000 and August 2020 were used. Data Extraction: All original research studies reporting at least 1 health outcomes associated with urban collective gardening in free-living adults from Western and other high-income countries were included. Of 1261 articles identified, 15 were included in the systematic review. Methodological quality was assessed by applying the criteria of the Quantitative Study Quality Assessment Tool. Analysis: A wide range of health indicators was used. Collective gardening was associated with higher fruit and vegetable consumption than was nongardening. Mixed results were found for physical activity and physiological health. A positive association was found in most studies with mental health and social health. However, the vast majority of included studies were cross-sectional and presented selection bias (n = 13 of 15 for both) and very few used objective measurement methods (n = 3 of 15). Conclusions: Longitudinal studies allowing the exploration of causal relationships are needed before the health benefits of collective garden participation suggested by existing studies can be confirmed.