Multigenerational family households rarely form out of environmental concern - or an intentional desire to be 'green'. More typically, they form because of financial pressures, caring responsibi1ities or to accommodate disruptions in extended families such as divorce or unemployment. Yet, they offer important, innate opportunities to reduce resource consumption. On a per capita basis, household size is inversely related to resource consumption and waste production. By housing more family members under one roof, multigenerational family living presents unheralded opportunities to save energy, water, building materials and land. Our ethnographic research with multigenerational family households in Wollongong, in the Illawarra region of southeastern Australia, explored the ways in which resources are consumed and shared in their rhythms of everyday life. These families inadvertently reduced their consumption of material resources by sharing space and everyday objects: white goods, furniture, cooking equipment, electronics, clothing, books, food, swimming pools and more. Although these sharing practices were not intentionally 'green', they nonetheless obviated the need for additional purchases to be made. At the same time, these households were sites of environmental debate and intergenerational leaming. 01der generations - while not identifying as environmentalists - sought to instil values of thrift among their younger relatives. They wanted to pass their inadvertent - or unintentional - sustainabilities onto their children and grandchildren. The term 'inadvertent sustainabilities' refers to practices not conceived with sustainability in mind, but which are environmentally beneficial nonetheless. Some younger household members, for their part, made persistent attempts to counter their parents' and grandparents' climate change skepticism, and to promote intentionally sustainable practices and purchases. Multigenerational family households thus provide fertile ground for the frugal (inadvertently 'green') practices and skills of older generations, and the intentional environmentalism of younger generations, to collide and coalesce - with profound implications for everyday domestic life. Throughout this chapter, we follow Blunt (2005) and Reid et al. (2010) in defining a household as a social unit occupying a single place or space of residence (the dwelling). Our definition of multigenerational family households is expansive. It includes adult children who have remained in - or returned to -the parental home (with or without their own spouse and children), and elderly parents living with one or more adult children. Additional relatives (whether aunts, uncles, grandparents or cousins) may be'added on' to an existing nuclear family unit. Each of these household configurations brings together related individuals in a manner distinct from single-parent or nuclear family living arrangements that involve one or more parents and their dependent child(ren). In so doing, they decrease the overall number of dwellings required to house an equivalent number of people. In the remainder of this chapter, we provide detail around the innate environmental benefits of larger households, before positioning our study within a broad body of cultural environmental research at the household scale. After outlining our research methods, we present empirical evidence of two types of sharing that take place in multigenerational family households - of space and material objects and more important, of ideas, skills and knowledge. Multigenerational family households engender opportunities to be inadvertently and deliberately 'green'. We conclude by taking our research findings to a further, speculative, step: in a climate-changing world, these households also hold important and unexplored potential for coping with environmental calamities.