The published studies of Louis Pasteur (1822-1895), Robert Koch (1843-1910), and especially Paul Ehrlich (1854-1915) referring to antibiosis, shows that in the early years of bacteriology they observed the effects of inhibiting agents on organisms. Alexander Fleming?s (1881-1955) publications on penicillin in 1928 was a milestone for medical history. As the antimicrobial compounds are discovered, it is thought that infectious diseases will be eliminated with the use of these antimicrobials. Unluckily, bacterial resistance to these antimicrobials quickly reduced this optimism and led the microbiology lab to develop test methods to determine sensitivity to these agents. Early researchers quickly understood that there were many variables affecting the results of antimicrobial susceptibility tests, and dozens of methods were developed and evaluated to standardize these variables. As a result, the need for standardization has directed many organizations to the production of standard antibiotic susceptibility tests methodologies, which are used today. In this review, the history and development of these methods are summarized to guide our colleagues.