The Université libre de Bruxelles (French, pronounced [ynivɛʁsite libʁ də bʁysɛl]; lit. Free University of Brussels; abbreviated ULB) is a French-speaking research university in Brussels, Belgium. It has three campuses: the Solbosch/Solbos campus (in the City of Brussels and Ixelles), the La Plaine/Het Plein campus (in Ixelles) and the Erasme/Erasmus campus (in Anderlecht).

The Université libre de Bruxelles was formed in 1969 by the splitting of the Free University of Brussels, which was founded in 1834 by the lawyer and liberal politician Pierre-Théodore Verhaegen. The founder aimed to establish a university independent from state and church, where academic freedom would prevail. This is still reflected in the university's motto Scientia vincere tenebras, or "Conquering darkness through science".

The ULB now has about 24,200 students, 33% of whom come from abroad, and an equally cosmopolitan staff.

Brussels has two universities whose names mean Free University of Brussels in English: the French-speaking Université libre de Bruxelles (ULB) and the Dutch-speaking Vrije Universiteit Brussel (VUB). Neither uses the English translation, since it is ambiguous.

The history of the Université libre de Bruxelles is closely linked with that of Belgium itself. When the Belgian State was formed in 1830 by nine breakaway provinces from the Kingdom of the Netherlands, three state universities existed in the cities of Ghent, Leuven and Liège, but none in the new capital, Brussels. Since the government was reluctant to fund another state university, a group of leading intellectuals in the fields of arts, science, and education — amongst whom the study prefect of the Royal Athenaeum of Brussels, Auguste Baron, as well as the astronomer and mathematician Adolphe Quetelet — planned to create a private university, which was permitted under the Belgian Constitution.

In 1834, the Belgian episcopate decided to establish a Catholic university in Mechelen with the aim of regaining the influence of the Catholic Church on the academic scene in Belgium, and the government had the intent to close the university at Leuven and donate the buildings to the Catholic institution. The country's liberals strongly opposed to this decision, and furthered their ideas for a university in Brussels as a counterbalance to the Catholic institution. At the same time, Auguste Baron had just become a member of the freemasonic lodge Les Amis Philantropes. Baron was able to convince Pierre-Théodore Verhaegen, the president of the lodge, to support the idea for a new university. On 24 June 1834, Verhaegen presented his plan to establish a free university.

After sufficient funding was collected among advocates, the Université libre de Belgique ("Free University of Belgium") was inaugurated on 20 November 1834, in the Gothic Room of Brussels Town Hall. The date of its establishment is still commemorated annually, by students of its successor institutions, as a holiday called Saint Verhaegen (often shortened to St V) for Pierre-Théodore Verhaegen. In 1836, the university was renamed the Université libre de Bruxelles ("Free University of Brussels").

After its establishment, the Free University faced difficult times, since it received no subsidies or grants from the government; yearly fundraising events and tuition fees provided the only financial means. Verhaegen, who became a professor and later head of the new university, gave it a mission statement which he summarised in a speech to King Leopold I: "the principle of free inquiry and academic freedom uninfluenced by any political or religious authority." In 1858, the Catholic Church established the Saint-Louis Institute in the city, which subsequently expanded into a university in its own right.