In this review, we introduce the biophysical and biochemical methods currently used to investigate the structures and stabilities of tetramolecular DNA G-quadruplexes containing chemical modifications. We hope this paper will guide others as they perform similar experiments leading to more information about the effects of chemical modifications on G-quadruplex formation. The structures of tetramolecular quadruplexes and some higher order structures based on tetramolecular quadruplexes are also described.