During the last 4 decades, intensive research has focussed on the effect of small organic molecules with antitumour activity that are able to intercalate into DNA and inhibit topoisomerase and telomerase enzymes. In this review, we describe some of the chemical and biological properties of acridine, which is a chemotherapeutic agent that has been used for cancer treatment since 1970. In addition, we summarise the progress that has been made in the development of anticancer agents based on the clinical in vivo/in vitro studies that have been conducted for 13 classes of natural and synthetic acridines.