Caught in the act: structural dynamics of replication origin activation and fork progression. LewisJacob S CostaAlessandro 2020 This review discusses recent advances in single-particle cryo-EM and single-molecule approaches used to visualise eukaryotic DNA replication reactions reconstituted in vitro. We comment on the new challenges facing structural biologists, as they turn to describing the dynamic cascade of events that lead to replication origin activation and fork progression.