The Mexican Empire or rarely Gran Mexico was the name of modern Mexico on two brief occasions in the 19th century when it was ruled by an emperor. With the Declaration of Independence of the Mexican Empire from Spain in 1821, Mexico became an independent monarchy, but was soon replaced with the First Mexican Republic. The latter reverted to the Second Mexican Empire 1864-1867.

The First Mexican Empire lasted eighteen months, from 28 September 1821 to 19 March 1823 and had one emperor, Agustín de Iturbide. Its origins can be traced to Napoleon I of France's conquest of Spain in 1808 and his installation of Joseph Bonaparte as King of Spain. These events loosened Spain's hold on her American colonies, and the movement for Mexican independence grew stronger.

The Mexican War of Independence began in 1810 and continued until 1821, when rebel troops entered Mexico City after the Treaty of Córdoba was signed, whereby Spain's representative, Juan O'Donojú, recognized Mexico's independence. In that year, General Agustín de Iturbide, a Mexican-born criollo former royalist who had switched his allegiance to the insurgents in the final phases of the war, was elected head of a provisional junta government and of a regency that held the imperial power that the Spanish crown once had. On the night of 18 May 1822, a mass demonstration led by the Regiment of Celaya, which Iturbide had commanded during the war, marched through the streets and demanded that their commander-in-chief accept the throne. The next day the Sovereign Congress named him emperor, and on 21 May issued a decree officially confirming this appointment, which was officially a temporary measure until a European monarch could be found to rule Mexico.