Dejima or Deshima, in the 17th century also called Tsukishima, was an artificial island off Nagasaki, Japan that served as a trading post for the Portuguese (1570–1639) and subsequently the Dutch (1641–1854). For 220 years, it was the central conduit for foreign trade and cultural exchange with Japan during the isolationist Edo period (1600–1869), and the only Japanese territory open to Westerners.

An artificial island is an island that has been constructed by humans rather than formed through natural processes. Other definitions may suggest that artificial islands are lands with the characteristics of human intervention in their format process, while others argue that artificial islands are created by expanding existing islets, constructing on existing reefs, or amalgamating several islets together. Although constructing artificial islands is not a modern phenomenon, there is no definite legal definition of it. Artificial islands may vary in size from small islets reclaimed solely to support a single pillar of a building or structure to those that support entire communities and cities. Archaeologists argue that such islands were created as far back as the Neolithic era. Early artificial islands included floating structures in still waters or wooden or megalithic structures erected in shallow waters.