Cells of all living organisms have evolved complex mechanisms to maintain genome stability. There is increasing evidence that spontaneous genomic instability occurs primarily during DNA replication. RecQ DNA helicases function during DNA replication and are essential for the maintenance of genome stability. In human cells, there exist five RecQ DNA helicases, and mutations of three of these helicases, encoded by the BLM, WRN and RECQL4 genes, give rise to the cancer predisposition disorders, Bloom syndrome (BS), Werner syndrome (WS) and Rothmund-Thomson syndrome (RTS), respectively. Individuals suffering from WS and RTS also show premature aging phenotypes. Although the two remaining helicases, RECQL1 and RECQL5, have not yet been associated with heritable human diseases, a single nucleotide polymorphism of RECQL1 is associated with reduced survival of pancreatic cancer, and RecQl5 knockout mice show a predisposition to cancer. Here, we review the functions of eukaryotic RecQ helicases, focusing primarily on BLM in the maintenance of genome stability through various pathways of nucleic acid metabolism and with special reference to DNA replication.