Galatasaray High School (Turkish: Galatasaray Lisesi, French: Lycée de Galatasaray), established in Istanbul in 1481, is the oldest and highly selective high school in Turkey. It is also the second-oldest Turkish educational institution after Istanbul University, which was established in 1453. The name Galatasaray means Galata Palace, as the school is located at the far end of Galata, the medieval Genoese enclave above the Golden Horn in what is now the district of Beyoğlu.

Admission to Galatasaray High School is determined through nationwide entrance examinations, with successful candidates representing the top 0.03% of students. The institution integrates elements of Turkish and French educational curricula, providing instruction in both languages and upholding a longstanding tradition of academic rigor.

The association football club Galatasaray S.K. was formed by and named after the institution, with the footballers in the club's formative years consisting entirely of pupils from the school. Galatasaray High School is the progenitor of the Galatasaray Community, which includes the football club, its parent Galatasaray Sports Club, and Galatasaray University.

Galatasaray has been the alma mater of numerous prominent figures in art, literature, diplomacy, politics, and other fields, with many Galatasaray alumni making notable contributions to their respective areas.

Sultan Bayezid II founded the Galata Sarayı Enderun-u Hümayunu (English: Galata Palace Imperial School) in 1481. The sultan often roamed the city, disguised as an ordinary citizen and legend has it that on one of these rambles he found a garden in Galata filled with beautiful red and yellow roses. In this garden, he met Gül Baba (English: Father Rose) of the Bektashi Order. The Sultan asked the wise man about how to improve the Empire and the city as they filled with immigrants. Gül Baba explained that he was happy with the city, his rose garden and the reign of the Sultan, but he would be even happier if there was a school which would educate students from this diverse range of backgrounds, as this would train the wise men needed to serve such a large Empire. He told the Sultan he would be proud to serve as a teacher in this school in order to create a generation of valuable subjects for the Empire. Bayezid II took Gül Baba at his word and returned to the garden weeks later with the edict which established the Ottoman Imperial School in the grounds next to the rose garden, with Gül Baba as its headmaster. Gül Baba became the first headmaster of Galatasaray and administered the school for many years. He died during the Ottoman raid on Hungary and his tomb is located in Budapest.

When the Ottoman army went to war, dervishes and minstrels accompanied it to provide prayers and entertainment but also armed themselves and joined in the fighting when necessary. Gül Baba was one of these dervishes.

Galata Palace Imperial School remained open until the 1830s, when the Tanzimat movement for reform and reorganisation drastically altered the Ottoman Empire's old establishment. Sultan Mahmud II replaced the Imperial School with the Ottoman Medical School, staffed largely by French professors with most courses taught in French. The Medical School was based in the Galatasaray (lit. Galata Palace) buildings for some thirty years.

The initial French name was Lycée Imperial Ottoman de Galataserai.