COSMOS is a cohort study of mobile phone use and health. The study will investigate the possible health effects of long-term use of mobile phones and other wireless technologies. It is an international study being conducted in five European countries – UK, Denmark, Sweden, Finland, the Netherlands and France. In the UK Imperial College London is carrying out this research. A pre-test took place in May 2009; 4,500 mobile phone users were invited to take part in the study.

The main launch of the study took place on 22 April 2010; 2.4 million UK mobile phone users were invited to participate. As of August 2010, 67,987 people were taking part in the UK arm of the study.

From February 2012 the UK study changes its eligibility criteria so that invitations were no longer mandatory to participate. Anyone aged 18 or over, who is a UK resident and uses a mobile phone can take part in the study.