The ILL was founded on 19 January 1967 with the signing of an agreement between the governments of the French Republic and the Federal Republic of Germany. The friendship and influence of Louis Néel and Heinz Maier-Leibnitz brought this project to fruition in Grenoble.

The ILL had the innovative status of a service institute, offering the scientific community the world's leading facilities in neutron science and technology - a large cold neutron source and ten neutron guides, each capable of serving three or four instruments with a very high intensity neutron flux...

In January 1973 the United Kingdom decided to join ILL and officially became the institute’s third Associate member country in 1974.

Twelve other countries have signed "Scientific Membership" agreements with ILL: Spain (1987- ), Switzerland (1988- ), Austria (1990- ), Italy (1997- ), the Czech Republic (1999- ), Sweden (2005- ), Hungary (2005-2013), Belgium and Poland (2006- ), Denmark and Slovakia (2009- ), India (2011-2014) and Slovenia (2020- ).

The Institute is an exceptional centre of excellence, a fine example of successful co-operation in Europe and a prototype for the European Research Area.