In 1971, with the conviction that Athens needed a truly International school The Hellenic international School in Athens (HIS) was founded, absorbing the English-speaking Ursuline Primary School. HIS offered American and British programs to international students from all over Athens and developed a high reputation for academics. A boarding school aimed mainly at expatriate families in the Middle East was established by the TASIS organization (The American School in Switzerland) in 1979, subsequently merging with HIS to form TASIS Hellenic International School. The addition of as many as 160 students from abroad gave TASIS Hellenic an even stronger international profile. The boarding program later was established in Varibobi at the charming "Auberge", and then at a traditional villa in Kifissia until 2005.

In 1998, the school became a part of the Basile Daskalakis Educational Organisation. When our sister school, International School of Larissa, was founded in 2003, the name of our school was changed to "International School of Athens" to better reflect the nature of the school and to create a unified identity for the two schools.