The trajectory of aging is profoundly impacted by the physical and social environmental contexts in which we live. While “top–down” policy activities can have potentially wide impacts on such contexts, they often take time, resources, and political will, and therefore can be less accessible to underserved communities. This article describes a “bottom–up”, resident-engaged method to advance local environmental and policy change, called Our Voice, that can complement policy-level strategies for improving the health, function, and well-being of older adults. Using the World Health Organization’s age-friendly cities global strategy, we describe the Our Voice citizen science program of research that has specifically targeted older adults as environmental change agents to improve their own health and well-being as well as that of their communities. Results from 14 Our Voice studies that have occurred across five continents demonstrate that older adults can learn to use mobile technology to systematically capture and collectively analyze their own data. They can then successfully build consensus around high-priority issues that can be realistically changed and work effectively with local stakeholders to enact meaningful environmental and policy changes that can help to promote healthy aging. The article ends with recommended next steps for growing the resident-engaged citizen science field to advance the health and welfare of all older adults.