Antibiotics are prescribed by dentists for treatment as well as prevention of infection. Systemic antibiotics in dentistry are limited and indicated only where there is local spread of the infection or where systemic upset has occurred. Antibiotics can be called as "life-saving drugs". However, inappropriate prescribing and excessive use of antibiotics are major factors in the emergence of antibiotic resistance. This book attempts to contribute to rational antibiotic use in endodontics, with a review of the general characteristics of these drugs.