Phenomenon of self-association of dyes in solutions has been considered. Different aspects of the phenomenon are discussed such as nature and the conditions of formation of dimers, aggregates and supramolecular ensembles; instrumental manifestation of self association of dyes; features of the phenomenon in aqueous systems; thermodynamics, kinetics and chemometrics of self-association. The monograph analyzes and summarizes more than 500 important publications about the self-association The book may be useful for researchers of chemistry and physics, students and postgraduate students.