Robin Holliday has made fundamental contributions to molecular genetics, epigenetics and cell biology. He postulated the intermediate in genetic recombination, the 'Holliday Structure', which is now accepted as integral to the process of recombination. His work on cellular aging implicated protein errors as being important in the aging process. His pioneering work in epigenetics and the role of DNA methylation has led to advances in our understanding of the importance of the epigenetic control of development.