The article considers the legal implications of a proposal by the Netherlands Government to build a new airport on an artificial island in the sea. The article concludes that the construction and use of an artificial island remains in principle within a coastal state's authority, with due regard to the rights and duties of other states and the LOS Convention and other rules of international law. Account must be taken of conflicting uses of the sea, for example, navigation, fishing, offshore activities, submarine cables and pipelines, and overflight. Freedom of overflight will be dealt with by the ICAO. With regard to other aspects of air law, such as liability and aviation security, there are no clear indicators of the appropriate course to take. The uniqueness of an airport at sea requires the Netherlands to tread new ground, requiring it to devise new ways for removing possible obstacles.