Guanine-rich sequences of DNA can form quadruply-stranded structures. It has been shown that folding single-stranded telomeric DNA into a quadruplex structure inhibits telomerase (an enzyme overexpressed in 85-90% of cancer cells). On the other hand, it has been hypothesised that the formation of quadruplex DNA structures in the promoter region of some oncogenes plays an important role in regulating the transcription of the corresponding gene. Consequently, there is great current interest in developing small molecules that can bind selectively to quadruplex DNA and in doing so could act as anticancer drugs. This review aims to discuss the different types of ligands that have been recently developed as quadruplex DNA stabilisers. The review is organised by the type of compound and mainly covers the literature between 2004 and 2007.