The Federal Constitution of the Swiss Confederation of 18 April 1999 (SR 101) is the third and current federal constitution of Switzerland. It establishes the Swiss Confederation as a federal republic of 26 cantons (states). The document contains a catalogue of individual and popular rights (including the right to call for popular referenda on federal laws and constitutional amendments), delineates the responsibilities of the cantons and the Confederation and establishes the federal authorities of government.

The Constitution was adopted by a referendum on 18 April 1999, in which a majority of the people and the Cantons voted in favour. It replaced the prior federal constitution of 1874, which it was intended to bring up to date without changing its substance.