The Ninth-of-May (1948) Constitution was the second constitution of Czechoslovakia, in force from 1948 to 1960. It came into force on 9 May, shortly after the communist seizure of power in the country on 25 February 1948. It replaced the 1920 Constitution.

Work on the new document had been underway since the summer of 1946. As a result, it was not a fully Communist constitution. It was superficially similar to its predecessor; indeed, several provisions were directly carried over from the earlier document. However, it contained a number of elements borrowed from the "Stalin Constitution" of the Soviet Union. The Soviet imprint on the final document was strong enough that President Edvard Bene refused to sign it and later resigned. It was flagrantly violated by the Communist Party of Czechoslovakia (KS), the government and many individuals throughout the period of its being in force, especially regarding the provisions on private ownership and human rights.

Since the country's liberation, there had been many disputes concerning nationalization, the relation of Czechs and Slovaks and other crucial issues. After the Communist take-over in February 1948, the Communist concept was largely applied. The constitution did not organize government administration under the Leninist principle of democratic centralism (a provision only incorporated in the following "socialist" 1960 Constitution of Czechoslovakia); indeed, it made no references to Communism or the KS. However, it did declare that Czechoslovakia had embarked on a "national and democratic revolution" that it intended to defend against "domestic and foreign reaction." It billed the 1948 coup d'etat as a defense of "the People's Democratic Order."

The constitution proclaimed Czechoslovakia a "people's democratic state" in which the people were "the sole source of all power." It declared that the economy of Czechoslovakia was based on nationalized industries, nationalized trade and a nationalized financial sector. The government sector was declared the basis of the economy, but it protected the private sector and cooperatives as well. It also granted a small degree of autonomy to Slovakia, which was given its own legislative body and governmental structure, although these were made subordinate to the central authorities in Prague. The parliament continued to be called the National Assembly, though the Senate was abolished.

Unlike most Communist constitutions, the Ninth-of-May Constitution did not replace the presidency with a collective body. It also afforded protections against arbitrary arrest; no one could be taken into custody without a warrant. On the other hand, the provisions enshrining civil rights were effectively neutered by a provision that forbade their use in order to make "statements and acts that constitute a threat to the independence, entirety, and unity of the State, the Constitution, the Republican form of government, or the People's Democratic Order" and allowed their restriction "when events occur that threaten in increased measure the independence, entirety, and unity of the State, the Constitution, the Republican form of government, and the People's Democratic Order, or public law and order." The constitutional guarantee of press freedom was rendered meaningless by provisions making movies and broadcasting state monopolies and giving the government sole power to decide who could publish periodicals. Judges were required to abide by both laws and government ordinances, thus taking away judges' right to strike down executive actions that did not accord with statutes.

Czechoslovakia, or Czecho-Slovakia (; Czech and Slovak: Československo, Česko-Slovensko), was a sovereign state in Central Europe, created in October 1918, when it declared its independence from Austria-Hungary.

In 1938, after the Munich Agreement, the Sudetenland became part of Germany, while the country lost further territories to Hungary and Poland. Between 1939 and 1945 the state ceased to exist, as Slovakia proclaimed its independence and subsequently the remaining territories in the east became part of Hungary, while in the remainder of the Czech Lands the German Protectorate of Bohemia and Moravia was proclaimed. In October 1939, after the outbreak of World War II, former Czechoslovak President Edvard Beneš formed a government-in-exile and sought recognition from the Allies.

After World War II, the pre-1938 Czechoslovakia was reestablished, with the exception of Carpathian Ruthenia, which became part of the Ukrainian SSR (a republic of the Soviet Union). From 1948 to 1989, Czechoslovakia was part of the Eastern Bloc with a command economy. Its economic status was formalized in membership of Comecon from 1949 and its defense status in the Warsaw Pact of 1955. A period of political liberalization in 1968, known as the Prague Spring, was violently ended when the Soviet Union, assisted by some other Warsaw Pact countries, invaded Czechoslovakia. In 1989, as Marxist–Leninist governments and communism were ending all over Eastern Europe, Czechoslovaks peacefully deposed their socialist government in 17th November 1989 in the Velvet Revolution, state price controls were removed after a period of preparation. In 1993, Czechoslovakia split into the two sovereign states of the Czech Republic and Slovakia.