The biology of the Common Tern (Sterna hirundo) has been studied on several continents, but information from central Asia is limited. Colony characteristics and nest site selection of Common Terns were studied in the desert and steppe of Mongolia to determine factors that influence their choices. Common Terns nested in marshy areas around small ponds, on sand bars adjacent to a lake in the Gobi, and on small islands in a water treatment plant in the steppe of Ulaanbaatar. In the Gobi, they nested with Pied Avocets (Recurvirostra avosetta) that defended the colony site, while the terns left. Common Terns selected colony sites surrounded by water and muck/ mud, and nest sites with good visibility. Their choice of colony and nest sites seemed to be a compromise between avoiding flooding, avoiding nest trampling by livestock, and finding any safe nesting place to avoid terrestrial predators.