In the face of the climate crisis and societal pressure, mega-event organizers and their international rights holders increasingly promote their sustainable credentials. Sustainability is now a commonplace term in mega-events, from the introduction of an environmental dimension into the planning of the 2000 Summer Olympic Games in Sydney, to the varying definitions of sustainability baked into the guiding principles of the IOC and the strategic documents of FIFA and many others. Concurrently, there is a burgeoning academic literature that investigates organizers’ claims of sustainability in terms of greenwashing, economic damage, unsupportable economic burdens, and damage to the social fabric of host cities. While illuminating the state-of-the-art in the extant literature on mega-events and sustainability, this chapter also identifies research gaps and suggests avenues for future research. These include calls for more coherent conceptual definitions of sustainability in order to establish comparisons across events in the post-Games period and a broadening of the conceptual umbrella so that studies on gentrification, legal exception, urban development and more might be analyzed from the perspective of (un)sustainability. Ultimately, the chapter advocates for a triple-baseline understanding of sustainability predicated on environmental, social, and economic dimensions.