Background: Ecological models posit that interactions among factors at multiple levels (e.g., individual, psychosocial, and environmental) influence physical activity (PA). However, interactions involving environmental factors are the least understood. Intervention studies also suggest PA behavior change may depend on the environments in which participants are encouraged to be active but such evidence from interventions targeting Latinos is limited. Methods: Chapter 2 tested interactions between neighborhood environmental and socio-demographic factors on total moderate-to vigorous physical activity (MVPA) among an international adult sample (N=10,258). Chapter 3 examined interactions between neighborhood environmental and psychosocial factors on context-specific PA among an adolescent sample from the Baltimore/Seattle regions (N=910). Chapter 4 assessed the moderating effects of neighborhood environmental factors on the impacts of a physical activity intervention targeting Latinas in San Diego, CA at 12-months post-intervention (N=319). Results: Chapter 2 found moderating effects by education and gender on the association between safety from crime and meeting high PA levels, with inverse associations found only among the high-education group and men. Education and gender moderated associations of safety from crime and the presence of transit stops with meeting minimum PA guidelines, with positive associations found for safety from crime only among women and the presence of transit stops only among men and the high-education group. Chapter 3 found moderating effects by decisional balance on the association between recreation facility density and neighborhood leisure-time PA among female adolescents, with a negative association found only among those with high decisional balance. Decisional balance also moderated the associations of neighborhood walkability with non-school MVPA among females and non-neighborhood leisure-time PA among males, with positive associations only among adolescents with high decisional balance. Chapter 4 showed higher total MVPA and leisure-time MVPA at 12-months post-intervention among participants with favorable perceived neighborhood aesthetics than those with less favorable evaluations. Conclusions: This dissertation supports the ecological models' hypothesized interactions between environmental and individual/psychosocial factors on PA and the moderating role of the neighborhood environment on the impacts of a multilevel PA intervention targeting Latinas. Findings support global efforts targeting multiple levels of influence to promote population PA, health, and environmental sustainability.