Fluoroquinolones are both old and new antimicrobial agents. The prototype agent of the class, nalidixic acid, was synthesized in 1962, whereas the new fluoroquinolones began to be used in the latter 1980s. During the past six years, orally administered fluoroquinolones have been used extensively in Japan and Europe to treat both community- and hospital-acquired infections. Most recently, one of the fluoroquinolones, ciprofloxacin, has also become available for parenteral and topical ophthalmic use. This article reviews the chemistry, antimicrobial activity, pharmacology, and clinical use of the fluoroquinolones.