Antimicrobials are some of the most commonly used drugs in veterinary medicine and have improved the health of food and companion animals alike. When properly performed and carefully analyzed, antimicrobial susceptibility testing is an invaluable component of evidence-based treatment of infectious disease. In the clinical setting, results should always be interpreted in the context of the patient. Antimicrobial susceptibility tests yield either categorical (susceptible, intermediate, or resistant) or quantitative (minimum inhibitory concentration [MIC]) data that can be categorically interpreted. Testing methods can be divided into two distinct categories, diffusion and dilution based. Categorical interpretation of antimicrobial susceptibility test results requires the development of clinical resistance breakpoints. Inducible resistance phenotypes pose unique diagnostic challenges; standard diffusion or dilution testing methods may fail to detect resistance. Interpretive reading plays a key role in identifying those phenotypes.