The Lycée Saint-Louis (French pronunciation: [lise sɛ̃ lwi]) is a selective post-secondary school located in the 6th arrondissement of Paris, in the Latin Quarter.

During the Wars of Religion, it emerged as a bastion of Catholicism, prompting Henri IV to confiscate the college's assets and remove its head.

The lycée is primarily devoted to the instruction of science (since 1885, the boarding school has exclusively admitted students pursuing scientific studies).

In 1843, a student from the school achieved a notable milestone by winning the first prize in mathematics at the concours général for the first time.

According to an old tradition now fully integrated to the school’s folklore, students admitted to Polytechnique are expected to express their gratitude to their alma mater by splashing the statue with red or yellow paint depending on whether the year is even or odd.

In addition to a dining hall, the school provides a cafeteria, and classrooms are available for student use outside their scheduled hours.