The identification of DNA as the genetic material and the elucidation of its structure by Watson and Crick [Watson and Crick, (1953) Nature (London) 171, 737–738], which has its 50th anniversary this year, first suggested the simple elegance with which the problem of passing on precise genetic information from one generation to the next could be solved. Semi-conservative replication is perhaps one of the simplest biological concepts to explain and understand. However, despite an enormous amount of effort in the intervening years, details of the way in which this process is regulated and performed are still unclear in many organisms. Recent work suggests that, due to their simplicity, the Archaea may make a good model for understanding some of the aspects of eukaryotic replication that still elude us.