The historical development of antibiotics has been summarized. Three distinct phases are discernible. The first (from historical times to about 1900) involved mostly folk remedies. The second (1900-c. 1940) was ushered in by Paul Ehrlich's development of the concept of 'selective toxicity' and saw the establishment of arsenicals and sulphonamides. The third, lasting to the present day, started with the exploitation of the pioneering studies of Fleming, Dubos and Waksman on antibiotic production by soil fungi. This latest phase has continued with the improvement of natural products by the skills of the medicinal chemist. The properties and evolution of three major groups of antibiotics, penicillins, cephalosporins and aminoglycosides are fully described. Finally, pathways of possible future evolution of antibiotics are outlined.