This chapter seeks to familiarize the readers with beta-lactam antibiotics. They have a β-lactam ring in their structure, for example penicillins, cephalosporins, monobactams, carbapenems. Penicillin is discovered by Alexander Fleming in 1928. Rigid cell wall of bacteria maintains integrity and shape. It protects from lysis due to osmotic pressure. Penicillins are classified into natural and semisynthetic. Natural penicillins include penicillin G (benzyl penicillin). Semisynthetic penicillins are produced to overcome limitations of natural penicillins. β-lactamase inhibitors, cephalosporins, carbapenems, and monobactams are the other topics which are covered in this chapter.