The Lisbon Regicide (Portuguese: O Regicídio) was the name given for the assassinations of King Dom Carlos I of Portugal and his heir, Prince Royal Dom Luís Filipe, Duke of Braganza, by assassins sympathetic to Republican interests and aided by elements within the Portuguese Carbonária, disenchanted politicians and anti-monarchists. The events occurred on 1 February 1908 in the Praça do Comércio, along the right margin of the Tagus River in Lisbon, more commonly referred to by its antiquated name: the Terreiro do Paço (or Palace Courtyard).

According to Jorge Morais, "the implantation of the [First] Republic in 1910 is not disassociated from the Regicide, which was cautiously and meticulously prepared, in contrast with the early thesis that it was the unplanned initiative of two anarchists." In fact, there were many factors that influenced the actions of the assassins.

Some idealistic students, politicians, free-thinkers and dissidents were inspired by the founding of the French Third Republic in 1870, and hoped that a similar regime could be installed in Portugal. The intellectual style was heavily middle class and urban, and hardly concealed its cultural mimicry of the French Republic. Most of the Republican leadership were from the same generation. Many were of the best educated in the country and were heavily influenced by the French positivist Comte and the socialist Proudhon, both democratic and nationalist. The ideology after 1891 was peppered with municipal autonomy, political and economic democracy, universal male suffrage, direct elections for legislative assemblies, a national militia instead of a professional army, the secularization of education, and the separation of Church and State, which were all tenets copied from French revolutionaries.