This chapter includes various classifications of antibiotics and the principles of antibiotic therapy. It also describes in details various antibiotics, such as β lactam antibiotics, Broad Spectrum antibiotics such as tetracyclines, macrolide antibiotics, antiviral antibiotics, and antimycotic agents. It also contains guidelines for antibiotic prophylaxis for various cardiac ailments given by American Heart Association (AHA) and American Dental Association (ADA).