Research showing the impacts of green space and ecosystem health on physical and mental health has significantly increased over recent years. While the specific mechanisms continue to be explored, the evidence is clear: the quantity and quality of green space, particularly those with high biodiversity and substantial tree canopy, are key to promoting health and livability in cities. Green space provides important habitat for native wildlife and mitigates the risks associated with a warming climate and rapid urbanisation. It reduces the health effects of noise and air pollution, improves social and economic wellbeing, encourages physical activity, fosters social connections and contact with nature, reduces stress, boosts mental health, and reduces mortality. Despite these known benefits, the design and delivery of green spaces that promote health and wellbeing in an equitable manner remains a challenge in rapidly growing and densifying cities. The need for higher-density, more compact urban development to accommodate population growth often comes at the expense of public and private urban green space. While there are growing greening policy commitments from governments, a concerning decline in these natural assets persists in many cities internationally, including in Australia. Several identified challenges that impact the greening of cities include: • The lack of economic incentives to prioritise green spaces over other land uses on both public and private land. • The lack of joined-up policy action and competing policy priorities with insufficient coordination across sectors and levels of government. • Inequitable distribution of green spaces across communities, contributing to health inequities. This chapter will explore these challenges by unpacking their underlying drivers, both internationally and within the Australian context. It also identifies potential levers and actionable strategies that can help retain, enhance, and deliver new urban green spaces that promote health and wellbeing.