The classes préparatoires aux grandes écoles (CPGE) (English: Higher School Preparatory Classes), commonly called classes prépas or prépas, are part of the French post-secondary education system. They consist of two years of study (extendable to three or exceptionally four years) which act as an intensive preparatory course (or cram school) with the main goal of training students for enrolment in one of the grandes écoles. The workload is one of the highest in Europe(29 to 45 contact hours a week, with up to 10 hours of guided tutorials and oral exam sessions).

Unlike most students in France who enroll in public universities directly after receiving a high school diploma, students from CPGE have to take national competitive exams to be allowed to enroll in one of the grandes écoles. These grandes écoles are higher education establishments (graduate schools) delivering master's degrees and rarely doctorates. They include science and engineering schools, business schools, the four veterinary colleges, the four écoles normales supérieures and the École Nationale des Chartes but do not include medical or law schools, nor architecture schools. Because of the competitive entrance exams, having attended one of the grandes écoles is often regarded as a status symbol, as they have traditionally produced most of France's scientists, executives and intellectuals (Écoles Normales Supérieures, École Polytechnique, Écoles des Mines, École nationale des ponts et chaussées, Télécom Paris, Écoles Centrales, HEC Paris, ESSEC Business School, ESCP Business School, Emlyon Business School, EDHEC Business School...).

Hence, there are three kinds of different prépas: scientific, economic and literary CPGE. Each of them prepare to pass the competitive exams of those grandes écoles.

Some preparatory classes are widely considered "elite", being extremely selective, and recruiting only the best students from each high school, if not the best student from each high school. These schools practically guarantee their students a place in one of the top grandes écoles. Among them are the Lycée Louis-Le-Grand, the Lycée Henri-IV, the Lycée Saint-Louis (these three are known as les trois lycées de la montagne), the Lycée Pierre-de-Fermat, the Lycée Stanislas and the Lycée privé Sainte-Geneviève.