The Constitution of the Republic of Croatia (Croatian: Ustav Republike Hrvatske) is the supreme legal act of the Republic of Croatia, serving as the basis for all other legislation.

While it was part of the Socialist Federal Republic of Yugoslavia, the Socialist Republic of Croatia had its own Constitution under the Constitution of Yugoslavia.

Following the first multi-party parliamentary elections held in April 1990, the Parliament made various constitutional changes. On December 22, 1990, they rejected the communist one-party system, adopted a liberal-democratic constitution and dropped the 'Socialist' label from the country's name, becoming the Republic of Croatia. The document is sometimes known as the Christmas Constitution (Božićni ustav).

The Constitution of 1990 used the semi-presidential model of the French Fifth Republic, with broad Presidential executive powers shared with the Government and a bicameral parliament which consisted of the House of Representatives and the House of Counties.

This is the preamble of the Constitution. It explains how the Croats managed to preserve their national identity throughout centuries in various forms of states from the formation of Croatian principalities in 7th century until present days.

The millenary identity of the Croatian nation and the continuity of its statehood, confirmed by the course of its entire historical experience within different forms of states and by the preservation and growth of the idea of a national state, founded on the historical right of the Croatian nation to full sovereignty, manifested in:

Considering the presented historical facts and universally accepted principles of the modern world, as well as the inalienable and indivisible, non-transferable and nonexhaustible right of the Croatian nation to self-determination and state sovereignty, including its fully maintained right to secession and association, as basic provisions for peace and stability of the international order, the Republic of Croatia is established as the nation state of the Croatian people and the state of the members of autochthonous national minorities: Serbs, Czechs, Slovaks, Italians, Hungarians, Jews, Germans, Austrians, Ukrainians, Rusyns, Bosniaks, Slovenians, Montenegrins, Macedonians, Russians, Bulgarians, Poles, Roma, Romanians, Turks, Vlachs, Albanians and the others who are citizens, and who are guaranteed equality with citizens of Croatian nationality and the realization of national rights in accordance with the democratic norms of the United Nations Organization and the countries of the free world. Respecting the will of the Croatian nation and all citizens, resolutely expressed in the free elections, the Republic of Croatia is hereby founded and shall develop as a sovereign and democratic state in which equality, freedoms and human rights are guaranteed and ensured, and their economic and cultural progress and social welfare promoted.

This chapter defines Croatia as unitary and indivisible democratic and social state in which power derives from the people and belongs to the people as a community of free and equal citizens. The people exercises this power through the election of representatives and through direct decision-making.