The International School Ibadan (ISI) was founded on October 14, 1963 and is located on the campus of the University of Ibadan. The school was founded as a joint project between the Ford Foundation and the University. It is a co-educational Boarding and Day School admitting boys and girls aged 9 to 19. It was primarily established to meet the need of finding a school with a standard comparable to schools in Europe and America for children of expatriates, living and working in Nigeria. It opened its doors to pupils of both expatriates and highly placed Nigerians. The social setting that ISI provided attracted more patronage from people of all races.

The first principal was Mr. S.D. Snell; followed by Mr. John Gillespie. The longest serving principal was an Anglican clergy, Archdeacon J.A.Iluyomade. He was also the first indigenous head of the school. After him was Rev. (Dr.) Dapo Ajayi, then Mr. Dapo Fajembola. Thereafter came the first female principal, Mrs. Esther Smith. After her was Mr. R.O. Akintilebo. The present principal (as at 2012) is Mr. M.B Malik.

I.S.I is well known for socials, extra-curricular activities like the International soiree (an event which comes up once every two years). The International soiree is an evening where all the nationalities represented among staff and students display the food, clothing and other material aspects of culture for sale with the objective of raising money for the less privileged. The Charity walk is another event that students use to raise money for the less privileged. Service to mankind is embedded in the culture of ISI. This tradition continues till this day.

The school has excelled academically over the years with its students maintaining top results in all examinations. ISI currently has a student population of 1400 and academic staff strength of about 120.