École polytechnique (also known by the nickname " X ") is a French public institution of higher education and research, located in Palaiseau near Paris. It is one of the French Grandes écoles, and is renowned for its four-year undergraduate Ingénieur Polytechnicien degree in science and engineering. Students are usually admitted after two years of selective university-level preparation in mathematics and physics or after a Bachelor of Sciences (Licence in French educative system).

Polytechnique was established in 1794 by the mathematician Gaspard Monge during the French Revolution, and became a military academy under Napoleon I in 1804. Today, the institution still runs under the supervision of the French ministry of Defence. Initially located in the Latin Quarter of central Paris, the establishment was moved in 1976 to Palaiseau on the Saclay Plateau, southwest of Paris.

Polytechnique is a founding member of ParisTech, a grouping of leading Paris-area engineering colleges established in 2007. In 2014 it became a founding member as well as the head of multidisciplinary technology and innovation institute, the confederal "University of Paris in Saclay". Among its alumni are three Nobel prize winners, one Fields Medalist, three Presidents of France and many CEOs of French and international companies.