Approximately 1% of the open reading frames in the human genome encodeproteins that function as DNA or RNA helicases. These enzymes act in all aspectsof nucleic acid metabolism where the complementary strands of DNA:DNA orDNA:RNA duplexes require to be transiently opened. However, they performwider roles in nucleic acid metabolism due to their ability to couple the energyderived from hydrolysis of ATP to their unidirectional translocation along strandsof DNA/RNA. In this way, helicases can displace proteins from DNA/RNA, drivethe migration of DNA junctions (such as the Holliday junction recombinationintermediate), or generate superhelical tension in nucleic acid duplexes. Here, wereview a subgroup of DNA helicase enzymes, the RecQ family, that has attractedconsiderable interest in recent years due to their role not only in suppression ofgenome instability, but also in the avoidance of human disease. We focusparticularly on the protein structural motifs and the multiple assembly states thatcharacterize RecQ helicases and discuss novel biophysical techniques to studythe different RecQ structures present in solution. We also speculate on the rolesof the different domains and oligomeric forms in defining which DNA structureswill represent substrates for RecQ helicase-mediated transactions.