Maximilian I (German: Ferdinand Maximilian Josef Maria von Habsburg-Lothringen, Spanish: Fernando Maximiliano Jos Mara de Habsburgo-Lorena; 6 July 1832 19 June 1867) was an Austrian archduke who reigned as the only Emperor of the Second Mexican Empire from 10 April 1864 until his execution on 19 June 1867. A member of the House of Habsburg-Lorraine, Maximilian was the younger brother of Emperor Franz Joseph I of Austria. He had a distinguished career as commander-in-chief of the Imperial Austrian Navy.

France, together with Spain and the United Kingdom, had invaded Mexico in the winter of 1861 to pressure the Mexican government into settling its debts with the three powers after Mexico had announced a suspension on debt repayment; the Spanish and British both withdrew the following year after negotiating agreements with the Mexican government and realising the true intention of the French, who sought to conquer the country. Seeking to legitimise French intervention, Emperor Napoleon III invited Maximilian to establish a new (pro-French) Mexican monarchy, which had been proposed numerous times in the past by Mexican monarchists. With a pledge of French military support and at the formal invitation of a group of the Mexican Conservative Party (monarchists hostile to the Liberal Party administration of President Benito Jurez), Maximilian accepted the crown of Mexico on April 10, 1864.The Empire managed to gain the diplomatic recognition of several European powers, including Russia, Austria, and Prussia. The United States, however, continued to recognize Jurez as the legal president of Mexico and saw the French invasion as a violation of the Monroe Doctrine, but was unable to intervene due to its ongoing civil war. Maximilian and his French allies never completely defeated the Mexican Republic; Republican forces led by Jurez continued to be active during Maximilian's rule. With the end of the American Civil War in 1865, the United States began providing more explicit aid to Jurez's forces. French armies began to withdraw from Mexico in 1866 in part due to the Austro-Prussian War. The Empire collapsed without French aid, and Maximilian was captured and executed by the restored Republican government in 1867.

The Emperor of Mexico (Spanish: Emperador de México) was the head of state and ruler of Mexico on two non-consecutive occasions in the 19th century.

With the Declaration of Independence of the Mexican Empire from Spain in 1821, Mexico became an independent monarchy—the First Mexican Empire (1822–1823). Mexico briefly reverted into a monarchy in the 1860s, during the Second Mexican Empire (1864–1867). In both instances of Empire, the reigning Emperor was forcibly deposed and then executed.