This chapter describes reference dilution (MIC) and disk diffusion antimicrobial susceptibility test methods for nonfastidious, aerobic bacteria. It describes CLSI (United States) and EUcst (European) reference methods and standardized disk diffusion methods. The procedure for performing each test type is described as well as quality control procedures. The advantages and disadvantages of each method are discussed. Finally, the most current interpretive breakpoint criteria for MIC and disk tests from the CLSI are listed.