Collège Marie-Thérèse was founded in 1903 soon after a law in France prohibitedreligious congregations of any persuasion. In its early years the Collège was attended by approximately sixty girls, mainly boarders, from across Europe. The 1950s and 1960s were a period of expansion for the school resulting in several major changes: co-education was introduced throughout the school, and the curriculum was modified in order to provide pupils with a more personal curriculum at the higher secondary level. In April 2001, the name of the school was changed to Institut International de Lancy. An English-language primary section was created the same year; an English-language secondary section followed in 2005. The schoolopened a bilingual section in 2007. Since the start of 2020–2021 school year, IIL has put in place the Kiva and anti-bullying programme for all students and staff. IIL is the first school in Switzerland to join the programme.