The ICRU (originally known as the International X-Ray Unit Committee and later as the International Committee for Radiological Units) was conceived at the First International Congress of Radiology (ICR) in London in 1925 and officially came into being at ICR-2 in Stockholm in 1928. The primary objective was to propose a unit for measurement of radiation as applied in medicine. From 1950 the ICRU expanded its role significantly to embrace a wider field. Initially meetings were held every 3 years at ICR congresses (excluding the 13-year period encompassing World War II) with one physicist and one radiologist from each participating country having the right of attendance with the Chair being nominated by the ICR host country. A permanent Commission was elected in 1953. L S Taylor (USA) served ICRU as a member [1928 – 1934] and then Secretary [1934 – 1953], first permanent Chair [1953 – 1969] and then Honorary Chair [1969 until his death in 2004]. Subsequent ICRU Chairs have been: H O Wyckoff (USA) [1969 – 1985]; A Allisy (France) [1985 – 1997]; A Wambersie (Belgium) [1997 – 2006]; P M DeLuca, Jr (USA) [2006 – 2009]; H-G Menzel (Germany) [2009 – 2018]. Vincent Grégoire is the current Chair.