Educate Together's first secondary school opened its doors to 45 First Year students on the campus of Nagle Community School, Mahon, which it is sharing on a temporary basis.
It is the first Educate Together school in the Munster area.
Cork ETSS joins four other Educate Together second-level schools opening this year in Dublin.
Principal Colm O'Connor said: “The school, which will be democratic, student-centred, co-ed and equality-based, will be in keeping, both with best practice in international educational thinking, as well as with the values of a rapidly evolving Irish society.
“We hope that this will be the first of many schools of this kind in the province as it offers greater choice to parents."