World-wide spread of bacterial resistance to antimicrobial agents may limit the future progress of medicine. A huge environmental antibiotic pressure, resulting from industrial production and marketing of these drugs, has simultaneously contributed to the increase in the diversity of resistant phenotypes, to the selection of the fittest among them, and to the dispersal of resistance genes, which is expected to result in a significant acceleration of the rate of microbial evolution. Current research is focused on the mechanisms involved in the genesis, selection and dispersal of resistance genetic determinants; strategies based on molecular epidemiology and mathematical models may contribute to control or reverse the frightening trend towards a new pre-antibiotic era.