Advancing global sustainability requires an understanding of ways in which rural-urban processes interact to produce sustainability outcomes. Rural-urban relationships are mostly studied through an urban focus and with urbanization as a main driver of sustainability outcomes. We review three broadly adopted perspectives on urban-rural relationships from an urbanization perspective. Then, we shift the conceptualization of rural-urban relationships away from 'the urban' to illustrate ways in which 'rural' processes, practices, and places drive rural-urban sustainability. We argue for a research agenda that analyzes 'the rural' and 'the urban' as mutually constituted. Such an understanding can inspire a new generation of infrastructure that integrates nature as essential for urban sustainability, supports diverse livelihoods and lifestyles, and helps to bridge rural-urban divides.