Any of a family of protein complexes that form at the origin of replication and function in replication restart in all organisms. Early complexes initiate double-stranded DNA unwinding. The core unit consists of a replicative helicase and a primase. The helicase further unwinds the DNA and recruits the polymerase machinery. The primase synthesizes RNA primers that act as templates for complementary stand replication by the polymerase machinery. The primosome contains a number of associated proteins and protein complexes and is part of the replication initiation process.