迪亚哥加西亚岛（Diego Garcia）是查戈斯群岛的主岛，也是英属印度洋领地首府所在地，距离印度最南端1900公里。位处太平洋与印度洋的重要国际水域，战略地位重要。

陆地面积约27平方公里；全岛为一珊瑚环礁，中央是澙湖，湖长24公里，宽6.4公里，北端有出口，是天然良港。

1532年葡萄牙人迪亚哥加西亚到达，1810年被英国占领，为英属毛里求斯属地，1965年成为英属印度洋领地的一部分。1966年英美签订协议后，成为美国在印度洋的重要海空军基地。

岛上有英美的联合军事基地，但主要是美军使用。由于军事原因，该岛无常驻居民，原住民被英政府驱逐。岛上有数种蟹类。

Diego Garcia is an atoll located south of the equator in the central Indian Ocean. Diego Garcia is the largest of the 60 small islands comprising the Chagos Archipelago. Diego Garcia was settled by the French in the 1790s and was transferred to British rule after the Napoleonic Wars. It was one of the "Dependencies" of the British Colony of Mauritius until it was detached for inclusion in the newly created British Indian Ocean Territory (BIOT) in 1965. Between 1968 and 1973, the population was forcibly removed by the United States through intimidation of locals and denying the return of any who left the island. Many were deported to Mauritius and The Seychelles, following which the United States built a large naval and military base on Diego Garcia, which has been in continuous operation ever since. As of March 2015, Diego Garcia is the only inhabited island of the BIOT; the population is composed of military personnel and supporting contractors.