Nationalization (nationalisation in British English) is the process of transforming privately-owned assets into public assets by bringing them under the public ownership of a national government or state. Nationalization usually refers to private assets or to assets owned by lower levels of government (such as municipalities) being transferred to the state. Nationalization contrasts with privatization and with demutualization. When previously nationalized assets are privatized and subsequently returned to public ownership at a later stage, they are said to have undergone renationalization. Industries often subject to nationalization include the commanding heights of the economy – telecommunications, electric power, fossil fuels, railways, airlines, iron ore, media, postal services, banks, and water – though, in many jurisdictions, many such entities have no history of private ownership.

Nationalization may occur with or without financial compensation to the former owners. Nationalization is distinguished from property redistribution in that the government retains control of nationalized property. Some nationalizations take place when a government seizes property acquired illegally. For example, in 1945 the French government seized the car-maker Renault because its owners had collaborated with the 1940–1944 Nazi occupiers of France. In September 2021, Berliners voted to expropriate over 240,000 housing units, many of which were being held unoccupied as investment property.

Economists can distinguish between nationalization and socialization, which refers to the process of restructuring the economic framework, organizational structure, and institutions of an economy on a socialist basis. By contrast, nationalization does not necessarily imply social ownership and the restructuring of the economic system. By itself, nationalization has nothing to do with socialism – historically, states have carried out nationalizations for various different purposes under a wide variety of different political systems and economic systems.