For most of the history of the Galactic Empire, Kalgan was a semi-tropical resort world in the Santanni Sector. Despite the breakdown of the Empire, Kalgan continued its prosperity under the rule of a series of princes. It was 7000 parsecs (22,820 lightyears) from Terminus.

The conquest by the Mule changed almost nothing about the mentality of its people. Asimov wrote that 'It alone of all that quadrant of the Galaxy seemed not to know that the Empire had fallen...' It devoted its entire economy to providing luxury. For all the decay around it, it continued to produce pleasure, and raked in cash. Because of it was so useful as a maker of money, its successive conquerors did as little as possible to harm it. The successive warlords seem to have gladly indulged in using that cash: the warlord ousted by the Mule wore a monocle, fur-lined scarlet robe, and a high-crowned hat.

Kalgan was the first planet taken over by the Mule in his string of conquest. After he defeated the Foundation, the Mule made it the capital of his 'Union of Worlds'. After the Mule died, Kalgan 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.

Its terrain seems to be perfect for a tourist planet: 'tamed jungles', 'mildly modeled shores', 'garishly glamourous cities'. Only a small number of places on Kalgan are known:

• Viceregal Palace—Palace of the Mule. The Kalganians believed that, when he died, the Mule directed that no-one enter the Palace until the Empire of the Galaxy is formed.
• Central Theatre—The largest Theatre in the Galaxy
• Kalgan Central Spaceport
• 'The Hangar'—An institution designed to deal with both the vast number of ships landing on Kalgan and with the need of tourists for living space. The hangar was a flat building several square miles large; a hotel for ships. Visitors to the hangar can take off to space at any time. The customer profits by combining hangar space and living accommodations into one bill; the owners profit by their huge profits; and the government profits by huge taxes. According to Asimov, the Hangar was an institution peculiar to Kalgan.

After its independence, Kalgan used the 'Kalganid' as its unit of currency.