The legal status of the edge of the sea has moved overtime. Originally, the edge of the sea was the land itself. This, however, is no longer the case. Now there is a legal regime in place that most States have agreed to on how the world’s seas and oceans ought to be organized. Consequently, the edge of the sea has become a series of arbitrary, imaginary lines beyond the land that ostensibly contain the power of States with bundles of rights and obligations for them found under the United Nations Convention on the Law of the Seas (UNCLOS). Basically, this chapter is three-fold. First, it begins with the internal locus of the State. It outlines the concept of sovereignty and how it will affect water-based urban developments within States’ jurisdiction as well as a governing principle for whatever societies transpire from these developments. Next, it examines the legal status of the world’s seas and oceans through the lens of UNCLOS to give those looking to make water-based urban developments beyond the horizon a basic understanding of the legal status and history of the areas that they may seek to inhabit or develop. Lastly, it addresses the legal status of water-based urban developments for now and moving forward.