The Constitutional Law of Federation was a constitutional law in Czechoslovakia adopted on 27 October 1968 and in force from 19691992, by which the unitary Czechoslovak state was turned into a federation.

The promulgation of the Constitutional Law of Federation amended fifty-eight articles of the 1960 Constitution of Czechoslovakia concerning the structure of government. The reform concerned Slovak autonomy; the concentration of governmental authority in Prague was a source of discontent within Slovakia throughout the 1960s, and the federalization of the Czechoslovak government codified in the 1968 constitutional amendments was virtually the only product of the reform movement associated with the Prague Spring to survive. The Czechoslovak state was declared to be composed of "two equal fraternal nations," the Czech Socialist Republic and the Slovak Socialist Republic, each with its own national administration paralleling and, at least in theory, equal in status to the federal government. Dual citizenship was established, and many of the former functions of the central government were instead placed under the jurisdiction of the two national governments. The federal government retained exclusive jurisdiction over foreign affairs, national defense, federal reserves, and national resources and held joint jurisdiction in a number of other matters, but the extent of the federalization reform was remarkably vast.

The most significant and lasting change under the 1968 constitutional law was the replacement of the unicameral National Assembly with a bicameral legislature known as the Federal Assembly. The two bodies, given equal authority, were the Chamber of the People, which was identical to the old National Assembly, and the Chamber of the Nations, which contained an equal number of Czechs and Slovaks. This institutional reform, together with a provision that certain decisions required the majority consent of each half (Czech and Slovak) of the Chamber of the Nations, was designed to end Slovak fear of Czech domination of the legislative branch of the government.

It soon became clear, however, that many aspects of the 1968 federalization were politically, as well as administratively, impractical. Political power remained firmly centralized in the KSC (proposals to federalize the party were dropped after the 1968 Soviet invasion in Czechoslovakia), and the administration of two economic systems, two police systems, and the like proved unworkable. As a result, July 1971 amendments to the 1968 Constitutional Law of Federation unified the administration of these and other government functions, ended the practice of dual citizenship and, most important, authorized the federal government to interfere with and invalidate measures of the national governments. Although most of the structures of the 1968 reform remained intact, observers of the Czechoslovak system of government in the 1970s agreed that federalism remained little more than a facade after the enactment of the 1971 constitutional amendments. In May 1975, the 1968 Constitutional Law of Federation was further amended to allow Gustav Husak to take over the presidency from the ailing Ludvik Svoboda.