Urban green spaces provide environmental, economic, societal and health benefits to cities. However, policy and planning interventions aiming to improve usage have often led to unintended consequences, including, in some circumstances, an actual decline in usage. Previous research has identified factors influencing the use of urban green space, more often with a focus on the ‘quality’ and physical features of the space, rather than on the broader social factors. This study aims to unpack the complexity of factors that influence the use of urban green space through the application of Systems Thinking. A qualitative mixed-method approach integrating System Dynamics with rapid ethnography was adopted to elicit the views of local residents in Thamesmead, London. A thematic analysis of interviews was undertaken to systematically map the causal relations between factors, which were compared to wider stakeholders’ views. Our findings highlight the relevance of dynamics and social influences on the use of green space, which include social interactions and stewardship, health conditions, availability of services and amenities. These are factors that are underexplored in the literature and, sometimes, overlooked in urban green space policy by decision-makers. We infer that attendance of urban green spaces requires time, which may be occupied in other practices determined by local conditions and needs. Expanding the spatial and temporal boundaries of investigation, wider than debates on ‘quality’, should, in our view, increase the chances of identifying critical influences and foster an increased use of green space.