The 1920s was the decade that started on January 1, 1920 and ended on December 31, 1929. It is sometimes referred to as the Roaring Twenties or the Jazz Age, when speaking about the United States, Canada or the United Kingdom. In Europe the decade is sometimes referred to as the "Golden Twenties" because of the economic boom following World War I.

Since the end of the 20th century, the economic strength during the 1920s has drawn close comparison with the 1950s and 1990s, especially in the United States of America. These three decades are regarded as periods of economic prosperity, which lasted throughout nearly each entire decade. Each of the three decades followed a tremendous event that occurred in the previous decade (World War I and Spanish flu in the 1910s, World War II in the 1940s, and the end of the Cold War in the late 1980s).

However, not all countries enjoyed this prosperity. The Weimar Republic, like many other European countries, had to face a severe economic downturn in the opening years of the decade, because of the enormous debt caused by the war as well as the Treaty of Versailles. Such a crisis would culminate with a devaluation of the Mark in 1923, eventually leading to severe economic problems and, in the long term, favour the rise of the Nazi Party.

Additionally, the decade was characterized by the rise of radical political movements, especially in regions that were once part of empires. Communism began attracting large numbers of followers following the success of the October Revolution and the Bolsheviks' determination to win the subsequent Russian Civil War. The Bolsheviks would eventually adopt a policy of mixed economics, from 1921 to 1928, and also give birth to the Soviet Union, at the end of 1922. The 1920s marked the first time in the United States that the population in the cities surpassed the population of rural areas. This was due to rapid urbanization starting in the 1920s.

The 1920s also experienced the rise of the far right and fascism in Europe and elsewhere, being perceived as a solution to prevent the spread of Communism. The knotty economic problems also favoured the rise of dictators in Eastern Europe and the Balkans, such as Józef Piłsudski in the Second Polish Republic and Peter and Alexander Karađorđević in the Kingdom of Yugoslavia. The devastating Wall Street Crash in October 1929 drew a line under the prosperous 1920s.