The quinolone class of antimicrobial agents has generated considerable interest since its discovery >40 years ago. Substantial progress has been made in our understanding of the molecular mechanisms of the action of quinolones against pathogenic bacteria, the induction of resistance to quinolones in these organisms, and the potential of each quinolone compound to induce toxicity in treated patients. Here, these key discoveries are reviewed; the present indications approved by regulatory agencies are described in detail, with comments on adverse events caused by quinolones in treated patients; and speculation about the future of the quinolones is proffered, even though their future is difficult to predict, because many factors may affect their clinical usefulness. However, the emergence of bacterial resistance to the quinolones is a major factor that will determine the future clinical effectiveness of these agents, so that intense investigation of mechanisms to either prevent or curtail resistance to quinolones is of prime importance to their future.