All the claimants in the South China Sea disputes have engaged in various degrees of island-building on many of the geographic features in the Spratly Islands. However, as noted by the Tribunal in the South China Sea Arbitration, none has been on the scale of Chinese island-building on the features which it occupies, which escalated after the Philippines initiated arbitral proceedings in 2013. While the most important aspect of the Award is that it clarified the extent of the respective maritime rights of China and the Philippines in the South China Sea, the Tribunal’s rulings on the reclamation and island-building activities of China are equally significant. To this end, this paper will examine the findings of the Tribunal on the legality of China’s island-building activities as well as legal constraints on such activities (if any). Last, it will explore the implications of these findings for the Southeast Asian claimants and island-building and fortification of the features that they occupy.