Quinolones act by inhibiting enzymes (topoisomerases) that are essential for DNA synthesis, and probably by fragmentation of chromosomal DNA. The bactericidal activity of these drugs depends on their concentration. Their spectrum has been broadened, particularly since the introduction of a fluorine atom at position 6 (fluorquinolones). Quinolones are used in a large variety of in-hospital and community infections, as the treatment of choice or as alternative therapy. Depending on the specific compound, they are used in urinary tract infections, sexually transmitted diseases, chronic osteomyelitis, respiratory tract infections, and severe systemic infections, among others. The emergence and spread of resistance to quinolones has limited their use in some conditions and may affect their application in the future. Strategies currently exist to minimize the spread of resistance. Quinolones are well tolerated and safe. The most common adverse effects involve the gastrointestinal tract and central nervous system.