This paper uses data from the English Longitudinal Study of Ageing to investigate the determinants of post retirement labour supply behaviour amongst retired men in England. I find the hazard of unretirement is highest when an individual is in their mid-late 60s. Evidence suggests unretirement is more likely amongst individuals with a higher level of educational attainment, who have a spouse in the labour market and are in better health. I investigate the nature of unretirement jobs and find they tend to be part time and provide a non-trivial source of income.