Antibiotics are magic bullets for many of us. The people who have suffered from deadly diseases and are saved only due to these antibiotics only know their relevance. Antibiotics are drugs which kill or slow the growth of bacteria. Antibiotics are one class of antimicrobials, a large group which also contains anti-viral, anti-fungal and anti-pyretic drugs. They are relatively harmless to host, therefore used for treating diseases. Initially the term antibiotic was only used for living organisms, however now term antibiotic is also used to synthetic antimicrobials like sulfonamides. Antibiotics are small molecules with lesser body weight and they are not enzymes. Some antibiotics are made from molds. Unlike the previous treatments available like poisons, antibiotics are more beneficial as they do not harm the host. Conventional antibiotics are not effective on viral, fungal and other non bacterial infections. Antibiotics are categorized on the basis of spectrum they cover. Antibiotics with wide range of coverage are known as wide spectrum antibiotics and antibiotics less coverage are known as narrow spectrum antibiotics. Action of each antibiotic varies with the site of action, ability of antibiotic to reach at that location and resistance development against that antibiotic. Some antibiotics kill the bacteria and they are known as bactericidal, where as other only stop the multiplication of bacteria so that body immune system can overcome them and they are known as bacteriostatic. www.geocities.com/arvindkatoch1