<p>There has been a rapid proliferation of systematic reviews exploring associations between the built environment (BE) and physical activity (PA). The objective of this study was to conduct a content analysis to synthesize the most commonly reported evidence gaps and limitations. Using text excerpts from systematic reviews, an inductive qualitative content analysis was conducted to identify and synthesize research gaps. Analysis involved three phases: 1) preparation (open coding using a hierarchical structure – grandparent, parent and child codes), 2) organization (codes applied to excerpts), and 3) interpretation (codes synthesized). From the 176 systematic reviews, 713 text excerpts describing gaps and limitations were extracted. A total of 157 codes were produced. Grandparent codes included BE features (<i>n</i> = 123 reviews), measurement (<i>n</i> = 101), PA types or domains (<i>n</i> = 53), populations and countries (<i>n</i> = 98), social environment (<i>n</i> = 49), and study design considerations (<i>n</i> = 155). The most common BE features gaps included BE measures (e.g., barriers, accessibility, quality), walkability, BE features (e.g., size, safety, aesthetics), green/natural spaces, rural, and active transportation infrastructure. BE features and study designs (experimental/longitudinal) was the most common intersection of evidence gaps. Findings identified a need for research using experimental and longitudinal designs. Most frequently cited gaps pertained to BE measures, walkability, green and natural spaces, rural, and active transportation infrastructure. This study serves to identify important gaps and limitations in previous research to help advance our understanding of what BE features promote PA and for whom.</p>