Kalgan is a "semi-tropical resort world" or vacation planet in Isaac Asimov's Foundation universe. Located 50 parsecs inward from Terminus, 7,000 parsecs from Haven and about 3,000 parsecs from Trantor, Kalgan continued its prosperity under the rule of a series of princes despite the breakdown of the empire.

Kalgan was one of the first planets taken over by the Mule in his string of conquests. After he defeated the Foundation, the Mule made it the capital of his Union of Worlds. After his death, the planet was ruled by a series of First Citizens from Han Pritcher to Stettin. The last of these, emboldened by the legacy of the Mule, launched a war against the Foundation. After the war ended in the defeat of Kalgan, the Kalganian Navy was dismantled, and the 27 worlds remaining in the Union were allowed to vote for return to the Union, full independence, or entry into the Foundation union.