A common step in prokaryotic recombination appears to be the synapsis of the 3′-end of single-stranded DNA with duplex DNA to form a D-loop. The enzymatic mechanisms by which 3′-ends are produced and by which D-loops are converted into recombinant molecules are illustrated by proposed mechanisms of recombination by the Escherichia coli RecBCD pathway and the phage λ Red pathway. The enzymes promoting recombination and the special DNA sites at which they act are emphasized. Recombination by other E. coli pathways and in other prokaryotes is compared with these mechanisms.Key words: Escherichia coli RecBCD pathway, phage λ Red pathway, Chi and cos sites, recombination enzymes.