The monograph examines the phenomenon of association of molecules and ions of dyes in solutions at a concentration level of interacting particles of 1 mimol or more. The spectral features of the heterogeneous association of some classes of dyes (triphenylmethane, rhodamines, cyanines, etc.), as well as the thermodynamic and equilibrium characteristics of nanosystems have been presented. The most probable structure of the associates was determined by molecular simulation methods.