The maintenance of genomic stability relies on the coordinated action of a number of cellular processes, including activation of the DNA-damage checkpoint, DNA replication, DNA repair, and telomere homeostasis. Many proteins involved in these cellular processes use different types of functional modules to regulate and execute their functions. Recent studies have revealed that many DNA-damage checkpoint and DNA repair proteins in human cells possess the oligonucleotide/oligosaccharide-binding (OB) fold domains, which are known to bind single-stranded DNA in both prokaryotes and eukaryotes. Furthermore, during the DNA damage response, the OB folds of the human checkpoint and DNA repair proteins play critical roles in DNA binding, protein complex assembly, and regulating protein-protein interactions. These findings suggest that the OB fold is an evolutionarily conserved functional module that is widely used by genome guardians. In this review, we will highlight the functions of several well-characterized or newly discovered eukaryotic OB-fold proteins in the DNA damage response.