Book excerpt: Antimicrobial agents are essential for the treatment of life-threatening infections and for managing the burden of minor infections in the community. In addition, they play a key role in organ and bone marrow transplantation, cancer chemotherapy, artificial joint and heart valve surgery. Unlike other classes of medicines, they are vulnerable to resistance from mutations in target microorganisms, and their adverse effects may extend to other patients (increased risk of cross-infection). As a consequence, there is a constant requirement for new agents, as well as practices that ensure the continued effective prescribing of licensed agents. Public awareness and concerns about drug resistant organisms has led to widespread publicity and political action in the UK, Europe and worldwide. The control of drug resistance and the implementation of good prescribing practice are now legal requirements in the UK as a result of the UK Health Act (2008). These fundamental changes underscore the need for a thorough understanding of the advantages and risks associated with specific antibiotic choices. This sixth edition of Antimicrobial Chemotherapy continues to be a valuable resource for undergraduates and graduates requiring a thorough grounding in the scientific basis and clinical application of these drugs. This new edition is updated to include the most recently licensed agents, notably in the treatment of viral infections including HIV/AIDS, and contains new guidance on prescribing practice and infection control practices that limit the development and spread of resistant organisms.