The Institute of Cancer Research (the ICR) is a public research institute and a member institution of the University of London in London, United Kingdom, specialising in oncology. It was founded in 1909 as a research department of the Royal Marsden Hospital and joined the University of London in 2003. It has been responsible for a number of breakthrough discoveries, including that the basic cause of cancer is damage to DNA.

The ICR occupies sites in Chelsea, Central London and Sutton, southwest London. The ICR provides both taught postgraduate degree programmes and research degrees and currently has around 340 students. Together with the Royal Marsden Hospital the ICR forms the largest comprehensive cancer centre in Europe, and was ranked first amongst all British higher education institutions in the Times Higher Education 2014 Research Excellence Framework Table of Excellence. In clinical medicine, 83% and in biological sciences, 96% of the ICR’s academic research was assessed to be world leading or internationally excellent (4* or 3*).

The annual income of the institution for 2015–16 was £162.1 million of which £61.7 million was from research grants and contracts, with an expenditure of £110.2 million. The ICR receives its external grant funding from the government body the Higher Education Funding Council for England, from government research council bodies and from charities including the Wellcome Trust, Cancer Research UK, Breast Cancer Now and Bloodwise. It also receives voluntary income from legacies and from public and corporate donations. The ICR also runs a number of fundraising appeals and campaigns which help support a variety of cancer research projects.