The National Institute of Open Schooling (often abbreviated as NIOS, NOS or National Open School), is the Board of Education for open schools in India. It was established by the Ministry of Human Resource Development of the Government of India in 1989Dead linkdate=June 2010 to provide education inexpensively to remote areas. The NIOS is a national board that administers examinations for Secondary and Senior Secondary examinations of open schools similar to the CBSE (Central Board of Secondary Education) and the CISCE (Council for the Indian School Certificate Examinations).

It had a cumulative enrollment of about 1.5 million students from 2004-2009 at Secondary and Senior Secondary levels and enrolls about 350,000 students annually which makes it the largest open schooling system in the world.