The 4-quinolone antibacterial agents have been under development and in use for over 25 years, but despite an enormous body of research work there are still many basic questions that remain unanswered. For example, we do not know how these agents kill susceptible cells - or even how the drugs interact with the target mol- ecule(s). However, we do know that the 4-quinolones display many properties which are not shared with any other group of antibacterial agents. This book raises the unanswered questions and assesses the potential significance to future chemotherapy of their unique features. The book also raises matters which are significant for physicians as well as for the pharmaceutical industry and the assessment of these agents by legislative bodies concerned with drug safety.