The development of antimicrobial resistance has led to the discovery of many natural mobile elements like transposons and conjugative plasmids. Integrons are carried on plasmids and transposons that potentially increase the dissemination of antibiotic resistance genes among bacterial species. Integrons are genetic elements containing the determinants of a site-specific recombination system. These DNA elements mediate the integration of antibiotic resistance genes into bacteria through the site-specific recombination. Integrons consist of an integrase gene (intl), a recombination site (attl), and one or two promoters responsible for expression of the inserted gene cassettes. Class 1 integrons are the most commonly studied and largely implicated type in the dissemination of antibiotic resistance among clinical isolates. In the last few years, a variety of new gene cassettes coding antibiotic resistance have been described. Having the ability of horizontal transfer of antibiotic resistance genes between interspecies of bacteria, integrons play a dominant role in the development of multiresistance in Enterobacteriaceae. In this review article, classification, structure and expression, epidemiology and clinical importance of integrons, has been discussed.