This entry explains nationalisation, the act of seizing private property by public authorities, in its theoretical and historical dimensions. The justification of seizure has developed historically reflecting the changes in the public-private interest dichotomy since Ancient Rome. Class struggle and its political repercussions in the era of capitalism have impacted the methods and practices of nationalisation, especially in its imperialist stage. The entry first summarizes the theoretical approach of Marxism-Leninism towards the political act of seizure. Nationalisation is correlated with concepts such as socialisation, collectivisation, expropriation, confiscation, which may overlap or differentiate according to the type and objective of seizure. Nationalisation is also discussed in the context of international law, particularly in terms of compensation, and in the context of economic planning versus market policies. The entry demarcates the history of nationalisation into two periods, 1917-1950 and 1950-2000. While the 1917 October Revolution and the transition to socialism characterises the first; decolonisation and sovereignty rights characterises the latter. Individual country experiences throughout the twentieth century are summarized including prominent nationalisation cases in Latin America, Africa, Asia, Europe and the Middle East. Finally, the entry elaborates the current discussions on denationalisation (or privatisation) under the influence of neo-liberalism and renationalisation under the influence of the crisis of capitalism, at the turn of the twentyfirst century.