In this review, based on my Garrod Lecture to the British Society for Antimicrobial Chemotherapy, I have given a brief outline of my career over the past 40 years, starting with research in the 1970s into the properties and functions of penicillin-binding proteins (PBPs), leading to the identification of the high molecular mass PBPs as the physiological targets of penicillin, and subsequent studies showing the emergence of low-affinity PBPs in penicillin-resistant clinical isolates by inter-species recombination and the generation of mosaic PBP genes. The studies of clinical isolates of gonococci, meningococci and pneumococci with PBP-mediated resistance to penicillin led to new interests in molecular epidemiology and the population and evolutionary biology of bacterial pathogens. The development (with colleagues) of multilocus sequence typing provided a method for the unambiguous characterization of bacterial strains that has proved to be very widely used, but the recent remarkable (and ongoing) developments in DNA sequencing technologies have provided the prospect of being able routinely to use whole genome sequences to characterize pathogen isolates. These developments will soon have major implications for diagnostic microbiology, outbreak investigations and our ability to follow the spread of strains of community-acquired and nosocomial pathogens at local, national and international levels. However, there are major barriers to be overcome, particularly with respect to how the avalanche of genome sequence data will be stored so that its transformative potential for molecular epidemiology and international public health are fully realized.