This chapter focuses on the impacts of megaprojects on the surrounding environment in six different cities (Tokyo, London, Paris, New York, Shanghai, and Riyadh). The chapter also analyzes some of the strategies used to develop allegedly “sustainable” megaprojects to counter environmental damage. The “greening” of megaprojects has become a widespread strategy for urban development worldwide. However, we contend that allegedly “sustainable” megaprojects follow the logic of strategically disinvesting in issues that appear secondary to the competitiveness of cities, while investing in issues that are crucial for forming urban regions as strategic centers for capital accumulation. Why are urban environmental policies frequently motivated by the goal of improving cities’ competitiveness or limiting elements (pollution, traffic, urban sprawl, etc.) that are likely to impair competitiveness? These policies are characterized by their thematic, social, and spatial selectivity by opting to pursue goals seen as win-win from an environmental and economic standpoint, and created to meet the aspirations of the middle and upper classes. Although the approach to sustainability used in “sustainable” megaprojects of “green capitalism” is a feasible strategy, it does not adequately address the main challenges posed by megaproject construction. We propose some essential elements to begin understanding megaproject sustainability as a complex, multidimensional concept.