Homologous genetic recombination occurs during the life cycle of virtually every organism Genetic studies especially in prokaryotes and fungi have defined the rules of recombination, led to the characterization of alternate pathways and to the development of molecular models The biochemistry of homologous genetic recombination has advanced most productively in bacteria and fungi due to the extensive genetic understanding of these organisms The identification of mutants defective in homologous recombination, purification and characterization of the gene products that participate in recombination has brought the ultimate goal of reconstituting a cell-k free system for Eschenchia coli, at least with naked DNA substrates, closer to reality.