ABSTRACT Accurate and timely genome replication is a universal feature of living organisms and a prerequisite for cell proliferation. In eukaryotes, genomic DNA replication initiates in two steps, origin licensing and origin firing, reflecting the loading and activation of the MCM replicative helicase motor on origin DNA. Biochemical reconstitution of these steps in the budding yeast model system signified a major advance towards understanding the molecular and structural details of eukaryotic replication initiation events. With recent successes in reconstituting origin licensing with purified human proteins, a mechanistic picture is beginning to emerge on how DNA replication initiates in higher eukaryotes and how it deviates from the paradigms established in budding yeast. In this review, we highlight similarities and differences in licensing mechanisms between yeast and metazoa.