In 2008, 115 pedal cyclists were killed and 2,450 reported as seriously injured on Britain’s roads, accounting for 9% of all killed or seriously injured (KSI) road casualties. The Government is committed to reducing road casualties for all road users, including cyclists, and has a national casualty target of reducing by 40% the number of people KSI in road collisions by 2010, compared with the baseline average for 1994-98. Whilst there is no specific target relating to cyclists, in 2004 the number of KSI had fallen to 38% below the baseline average. However, the number of KSI has increased steadily since then and in 2007 and 2008 was 31% below the baseline average. The Department for Transport commissioned research to assess the causes of collisions involving cyclists. This report investigates the key causal factors relating to accidents involving cyclists. The work involved an international literature review and a detailed analysis of cyclist casualties in Great Britain, drawing on both national and in-depth databases of road collisions and cycling. The main source of the casualty data was the national STATS19 injury accident data for 1994-2007. Contributory factor data has been recorded nationally as part of the STATS19 system from 2005 and is also reported. The main source of cycling activity data was the National Travel Survey (NTS).