In the fifty years since the inception of the Society for General Microbiology the study of pathogenic microbes and the development of methods for their control have been a focus of attention for many microbiologists. This volume reviews the immense progress which has been made during the past half-century, opening with the text of Sir Alexander Fleming’s 1946 Linacre Lecture Chemotherapy: Yesterday, Today and Tomorrow, and then drawing together contributions which consider the development of key antimicrobial compounds, both naturally occurring and synthetic, active against bacteria, viruses, fungi, and protozoa. Broader issues of antimicrobial production, screening, improvement, and resistance are also considered. Topics such as why epidemics still occur and the need for new antibiotics highlight the fact that, despite the advances, the fight against infection continues unabated.