This chapter explores the intersection of age-friendliness and environmental sustainability in Japanese cities and communities, a topic of increasing urgency given Japan’s rapidly ageing population and escalating climate challenges. As of 2024, over 29% of Japan’s population is aged 65 and older, and the country also faces rising greenhouse gas emissions and frequent natural disasters. These dual pressures demand integrated approaches to urban development that simultaneously promote healthy ageing and environmental resilience. Drawing on national frameworks such as the WHO’s Age-friendly Cities and Communities (AFCC) model and the United Nations’ Sustainable Development Goals (SDGs), the chapter outlines how Japanese policy and practice have begun to merge these agendas. Through a multidisciplinary lens incorporating urban planning, social policy, and environmental science, the chapter analyses conceptual overlaps and gaps between age-friendly and sustainable cities. Case studies from Akita City, Kanagawa Prefecture and Takarazuka City illustrate local innovations in inclusive design, green infrastructure and participatory governance. The role of community engagement and social capital is emphasised, showcasing how older adults contribute to co-creating resilient and livable environments. National and local policy efforts, including Smart City initiatives and urban development ordinances, are examined alongside challenges such as institutional fragmentation and technological accessibility. The chapter concludes by advocating for holistic, cross-sectoral governance and intergenerational collaboration to realise inclusive, climate-resilient urban futures. Japan’s experience offers valuable insights for other ageing societies navigating similar environmental and demographic transitions, positioning it as a testing ground for globally relevant urban strategies.