An accessible introduction to how genomics has and will provide novel methods for bacterial investigation and advance our understanding and knowledge of bacterial pathogenicity. The authors critically evaluate the applications of genomics to diagnostic bacteriology, highlighting both current and likely future uses, describing real-time PCR methods, and outlining the promise of microarrays in clinical bacteriology. Their discussion examines in detail genomic approaches to antibacterial discovery, the nature of pathogenicity, the discovery of new pathogens, the exploration of the concept of clonality in bacteria, and bacterial taxonomics.