G-quadruplexes are a family of four-stranded structuresstabilized by guanine quartets, in which four planar guaninesestablish a cyclic array of hydrogen bonds. They are ofspecial interest due to the increasing evidence for theirformation in vivo and their possible implication in biology,especially at telomeres and as contributors to gene regulation.Moreover, G-quadruplexes are also formed as a result ofself-assembling processes of guanosine derivatives, yieldingseveral interesting motifs such as G-ribbons and G-wireswhich have peculiar electrical conductivity properties thatare being explored as molecular wires.This special issue is initiated with two articles discussingthe self-assembling properties of guanosine derivatives whichdescribe the basic principles of G-quadruplex formation. Thefirst article by Neviani et al. analyzes the presence of severallevels of organization of guanosine derivatives carryingone or two lipophilic units as observed by light scatteringtechniques and transmission electron microscopy (TEM)experiments. The second article by Mariani et al. describesa study on quadruplex formation of 2 -deoxyguanosinemonophosphate by small-angle X-ray scattering techniques.