AbstractEver since the structure of DNA was made clear by Watson and Crick and their guess about the general mechanism of DNA replication shown to be correct by Meselson and Stahl, there has been great uncertainty about the mechanics of the process that expeditiously separates the two strands of the double helix during DNA replication. These uncertainties are most acute in the case of the bacterial chromosome, because it is apparently both the longest DNA molecule known (and therefore the one most subject to mechanical problems) and, in terms of nucleotides per second, the most rapidly replicated. Nevertheless, there are some facts that bear upon the mechanical aspects of DNA replication in bacteria (and elsewhere), and these are reviewed in this article.