Replicative single-stranded DNA gaps are emerging as central intermediates in the cellular response to replication stress. Replication frequently continues past lesions or difficult-to-replicate regions through leading-strand repriming or delayed Okazaki fragment (OKF) maturation, generating structured gaps requiring stabilization and repair. Here, we describe the major routes of gap formation, including polymerase-helicase uncoupling, impaired OKF processing, PrimPol-mediated lesion bypass, and...