Providing a state-of-the-art reference on a field undergoing exponential growth, G-Quadruplexes addresses the topology and structural characteristics of quadruplexes, their interactions with small ligands and biologically relevant cations and proteins, their possible biological roles, and the potential small-ligand (metal-containing) drugs that have developed from their studies. The seasoned author team explore the multiple roles of G-quadruplexes in different chapters, including the important topic of RNA quadruplexes, target cellular structures (RNA and the telomere), and in vivo studies, as well as challenges, perspectives, and future directions of research.