It is a coral island built by accumulation of coral polyps and algae. If the coral is for some reason raised above sea level it dies and together with other debris forms  a strip of land. Christmas Island probably had a very much larger lagoon than appears at present but it is being reduced in size by new coral banks and by accumulated debris

The Island was discovered by Captain James Cook on Christmas Eve, 1777, and "as we kept Christmas here, I called this discovery Christmas Island".

The Polynesian natives in their search for new lands passed the island but did not attempt to settle on it for ant length of time. British and American whalers occasionally visited the island. In 1902 Levers Pacific Plantations Ltd. planted 70,000 coconut trees before deciding to  abandon the island..

In 1942 American troops landed and at one time 10,000 were on the island. They constructed airstrips and dredged a channel to enable supply ships to enter the lagoon. They left the island in 1948

At present the island is under the control of the District Commissioner for the Northern Line Islands and is eventually to be developed as a permanent Royal Air Force Base.