During the proteomics period, the growth in the use of recombinant proteins has increased greatly in the recent years. Bacterial systems remain most attractive due to low cost, high productivity, and rapid use. However, the rational choice of the adequate promoter system and host for a specific protein of interest remains difficult. This review gives an overview of the most commonly used systems: As hosts, Bacillus brevis, Bacillus megaterium, Bacillus subtilis, Caulobacter crescentus, other strains, and, most importantly, Escherichia coli BL21 and E. coli K12 and their derivatives are presented. On the promoter side, the main features of the l-arabinose inducible araBAD promoter (PBAD), the lac promoter, the l-rhamnose inducible rhaP BAD promoter, the T7 RNA polymerase promoter, the trc and tac promoter, the lambda phage promoter p L , and the anhydrotetracycline-inducible tetA promoter/operator are summarized.