Mega sporting events like the Olympic and Paralympic Games and FIFA World Cup can come at significant environmental costs due to the construction of infrastructure and sports venues and the travel of athletes and spectators. In light of this potential impact, event organisers are endeavouring to promote environmental stewardship through smart facility design, concerted educational campaigns, and a formalised long-term environmental legacy plan. In this chapter, we provide an historical summary of environmental issues related to mega-events. Additionally, we highlight several examples of sport’s largest international sporting events and compare their pre-event legacy development with post-event environmental impact analyses. We conclude the chapter by outlining the challenges that come with planning and operating a mega-event, many of which come long after the event has ended.