A maritime boundary is a conceptual division of the Earth's water surface areas using physiographic or geopolitical criteria. As such, it usually includes areas of exclusive national rights over mineral and biological resources, encompassing maritime features, limits and zones. Generally, a maritime boundary is delineated through a particular measure from a jurisdiction's coastline. Although in some countries the term maritime boundary represent borders of a maritime nation and are recognized by the United Nations Convention on the Law of the Sea, they usually serve to identify international waters.

Maritime boundaries exist in the context of territorial waters, contiguous zones, and exclusive economic zones; however, the terminology does not encompass lake or river boundaries, which are considered within the context of land boundaries.

Some maritime boundaries have remained indeterminate despite efforts to clarify them. This is explained by an array of factors, some of which illustrate regional problems.