The reported increase in the occurrence of antibiotic-resistant bacteria serves to emphasize the importance of accurate susceptibility testing. This timely guide examines the role of the clinical microbiology lab in integrated patient care. The first section addresses basic susceptibility disciplines such as macro and microbroth dilution, agar dilution, and disk diffusion. The second section considers susceptibility protocols that may be performed by a subset of labs, and describes the testing of fastidious organisms. The third section covers antibiotic development and discusses antibiogram design and use. It includes a table of antibiotic classes and common drug-bug susceptibilities.