To survive and proliferate, cells have to faithfully segregate their newly replicated genomic DNA to the two daughter cells. However, the sister chromatids of mitotic chromosomes are frequently interlinked by so-called ultrafine DNA bridges (UFBs) that are visible in the anaphase of mitosis. UFBs can only be detected by the proteins bound to them and not by staining with conventional DNA dyes. These DNA bridges are presumed to represent entangled sister chromatids and hence pose a threat to faithful segregation. A failure to accurately unlink UFB DNA results in chromosome segregation errors and binucleation. This, in turn, compromises genome integrity, which is a hallmark of cancer. UFBs are actively removed during anaphase, and most known UFB-associated proteins are enzymes involved in DNA repair in interphase. However, little is known about the mitotic activities of these enzymes or the exact DNA structures present on UFBs. We focus on the biology of UFBs, with special emphasis on their underlying DNA structure and the decatenation machineries that process UFBs.