MICCAI 2009, the 12th International Conference on Medical Image Computing and Computer Assisted Intervention, was held from 20th to 24th September 2009 in London, UK, organised jointly by research teams at Imperial College, University College London (UCL), University of Oxford and University of Manchester. MICCAI attracts annually world leading scientists, engineers and clinicians from a wide range of disciplines associated with medical imaging and computer assisted surgery. The venue for MICCAI 2009 was located at the main campus of Imperial College London in South Kensington. It is situated in one of London's finest locations, adjacent to landmarks such as The Royal Albert Hall and the Science, Natural History and Victoria & Albert Museums, with Hyde Park just a short walk away.