Psychosocial oncology is a multi-disciplinary field of practice and, as a recently developed speciality, covers the psychological, social and behavioural dimensions of cancer. We describe the historical background and changing ethos in medical practice in order to understand factors that contributed to the emergence of this new discipline. Modern psychosocial oncology covers a number of topics; the diagnosis and management of psychological morbidity and distress across the cancer continuum from diagnosis through survivorship and, for some patients, terminal illness, the recognition that behaviour and lifestyle contribute to cancer risk and prognosis, the need to include families and carers alongside patients in a comprehensive model of supportive cancer care. Best practice, based on evidence and nationally and internationally accepted guidelines, is being integrated into national cancer plans, and services are briefly described. Future challenges include the need to recognize that the behavioural and mental health sciences have a role to play in comprehensive cancer care and that multi-disciplinary care, which includes psychosocial care, is the best model for ensuring patients needs are comprehensively and adequately met. The return of modern medicine to a more holistic person-focused ethos is needed in order to put the patient back into patient-centred cancer care.