GUM is the main department store in many cities of the former Soviet Union, known as State Department Store during the Soviet era. Similarly named stores operated in some Soviet republics and in post-Soviet states.

A department store is a retail establishment offering a wide range of consumer goods in different areas of the store, each area ("department") specializing in a product category. In modern major cities, the department store made a dramatic appearance in the middle of the 19th century, and permanently reshaped shopping habits, and the definition of service and luxury. Similar developments were under way in London, in Paris and in New York City (Stewart's).