The origin of replication (also called the replication origin) is a unique DNA sequence at which DNA replication is initiated. DNA replication may proceed from this point bidirectionally or unidirectionally.

The specific structure of the origin of replication varies somewhat from species to species, but all share some common characteristics. The origin of replication binds a member of the pre-replication complex—a protein complex that binds, unwinds, and begins to copy DNA.

Prokaryotes have a single circular molecule of DNA, and typically only a single replication origin. Eukaryotes often have multiple origins of replication on each chromosome. Having many origins of replication helps to speed the duplication of their (usually) much larger store of genetic material. The segment of DNA that is copied starting from each unique replication origin is called a replicon .

Origins of replication are typically assigned names containing "ori". For example, the E. coli replication origin is known as oriC.