Carlism (Basque: Karlismo; Catalan: Carlisme; Galician: Carlismo; Spanish: Carlismo) is a Traditionalist and Legitimist political movement in Spain aimed at establishing an alternative branch of the Bourbon dynasty, one descended from Don Carlos, Count of Molina (1788–1855), on the Spanish throne.

The movement was founded as a consequence of an early 19th-century dispute over the succession of the Spanish monarchy and widespread dissatisfaction with the Alfonsine line of the House of Bourbon, and subsequently found itself becoming a notable element of Spanish conservatism in its 19th-century struggle against liberalism, which repeatedly broke out into military conflicts known as the Carlist Wars.

Carlism was at its strongest in the 1830s. However, it experienced a revival following Spain's defeat in the Spanish–American War in 1898, when the Spanish Empire lost its last remaining significant overseas territories of the Philippines, Cuba, Guam, and Puerto Rico to the United States.

Carlism continued to play a notable role in the 20th century as part of the Nationalist faction in the Spanish Civil War and the subsequently triumphant Francoist regime until the Spanish transition to democracy in 1975. Carlism continues to survive as a minor party:

Objectively considered, Carlism appears as a political movement. It arose under the protection of a dynastic flag that proclaimed itself "legitimist", and that rose to the death of Ferdinand VII, in the year 1833, with enough echo and popular roots, ... they distinguish in it three cardinal bases that define it:
a) A dynastic flag: that of legitimacy.
b) A historical continuity: that of Las Españas.
c) And a legal-political doctrine: the traditionalist.

— ¿Qué es el Carlismo?

Traditionally, all but one of the Spanish kingdoms allowed the succession of daughters in the absence of sons and of sisters in the absence of brothers (male-preference primogeniture). The one exception, Aragon, tended to favour semi-Salicism. The most elaborate rules formed the "Seven-part code" (Siete partidas) of the late 13th century.

On 1 November 1700 a French Bourbon prince, Philip V, acceded to the Spanish throne. In the French royal house, Salic law applied, which did not permit female succession. Accordingly, the traditional Spanish order of succession had to give way to a semi-Salic system, which excluded women from the crown unless all males in the agnatic descent from Philip, in any branch, became extinct. It is not implausible that this change might have been enacted at the insistence of a hostile foreign power, as the scenario of such a union could impinge profoundly on questions of national importance (particularly among states that preferred to maintain their distance from policy positions occupied by the Franco-Spanish consensus, of which the Holy Roman Empire was one). Some disagreement on this topic was evident for a number of years, even after it became clear that any question of a Franco-Spanish union was a political non-starter.