Me self-assembly and lyotropic mesomorphism of guanosine derivatives are reviewed. Natural and synthetic guanosine nucleotides self-assemble into columnar aggregates based on G-quartets; at the appropriate concentrations these aggregates form, in water, lyotropic mesophases of the cholesteric and hexagonal type. Lipophilic derivatives undergo different types of self-assembly in the presence of alkali metal ions they form, in organic solvents, columnar structures and lyomesophases similar to those observed for the hydrophilic derivatives; in the absence of ions they form instead ribbon-like aggregates which give rise to new types of lyotropic phases. The ribbon-like aggregates have interesting electrical properties.