Antibiotics are considered as powerful medicines that treat certain infections. They play a vital, role in saving the lives of the patients either by stopping bacteria from reproducing or by destroying them. The first antibiotic developed was penicillin. The chapter deals with various antibiotics used in dental practice. A range of antibiotics are classified, according to chemical structure, mechanism of action, spectrum of activity, mode of action, and source. Problems associated with antibiotic usage include toxicity, hypersensitivity reactions, drug resistance, superinfection, nutritional deficiencies, and masking of an infection. Factors required for antibiotic selection include patient’s factors like age, renal function, hepatic function; local factors like drug allergy; impaired host defence like in pregnancy; and genetic factors. Indications for antibiotics prophylaxis and adult dosage of commonly used antibiotics in dental office are also discussed in this chapter.