Rapidly emerging drug resistance in all classes of pathogenic microorganisms has become a challenging task and a global health issue in recent years. There are very limited alternative options available to cure infectious diseases, as the rate of rise in drug resistance in infectious agents is higher than the arrival of new antimicrobial drugs. There is a dire need to look for new types of anti-infective agents, besides looking for new antibiotics. One of the promising types of antimicrobial agents is aptamers, synthesized through systematic evolution of ligands by exponential enrichment (SELEX) technique. Aptamers hold a significant promise for the treatment of various infectious diseases in the future. In the recent past, a number of successful attempts have been made to select and apply aptamers for the detection and binding of infectious agents and their products for therapeutic purposes. This chapter presents a basic introduction to aptamers and their application as anti-infective agents.