Bacteriophages (phages) are arguably the most abundant biological entities on the planet. They play crucial roles in driving the adaptive evolution of their bacterial hosts, and achieve this both through the predator-prey roles of the phage-bacterium interaction and through the adaptive impacts of lysogeny and lysogenic conversion.  Bacteriophages are the source of many biochemical reagents and technologies, indispensible for modern molecular biology. Furthermore, phages are being exploited in other areas of biotechnology, including diagnostics, prophylaxis and other aspects of food microbiology. In recent years there has been a growing interest in developing phages for therapeutic purposes (phage therapy) as natural alternatives to antibiotics. The inexorable rise in the incidence of antibiotic resistance in bacterial pathogens, coupled with the disappointingly low rate of emergence of new, clinically useful antibiotics, has refocused attention on the potential utility of phages for treating human and animal disease. Examples of the roles of phages in fundamental biological research and in medical and industrial biotechnologies will be discussed at this meeting