An approach to the investigation of the thermodynamic and kinetic stability of variable-valence metal complexes has been developed. Concepts of the generalised inverse problems of quantitative instrumental analysis and the complex formation equilibria are introduced. The procedure for this investigation is regarded as a sequential procedure for solving these two inverse problems. The classical methods for investigating the complex formations in solution are analysed in terms of these in-verse problems. Their generalisations are given to determine together with the formation constants also redox-decomposition rate constants of variable-valence metal complexes and the rate law of numerous redox processes, for which the rate-determining step is the decay of an intermediate complex, are presented. Classification is discussed and their implementation on the examples of the study of the complexation and in-tramolecular redox decomposition of cerium(IV) hydroxo complexes with some dicarboxylic, oxycarboxylic acids and aliphatic polyatomic alcohols in dependence on acidity (pH 0.73.4) of a sulphate medium at the ionic strength I=2 and temperatures of 10.043.0 C by UV-Vis spectroscopy and pH measurements. The region of existence, composition, ligand speciation, stability constants of the complexes [CeOH(H-xR)n]3-nx, rate constants, and activation energies of the intramolecular redox decomposition were determined for these complexes on the sulphate background. The rate law of the redox process occurring in the studied systems on the basis of the calculated constants and set of all the chemical and algebraic equations describing the equilibria in systems is derived, and the quantitative model of this process is created. The existence of positive correlation between thermodynamic and kinetic stability of the complexes [CeOHH-xR]3-x with x > 2 and its absence for x > 2 was found on the sulphate background. Discussed also are the computational aspects of solving the regarded generalised problems. This book is well-suited for researchers in the chemistry of co-ordination compounds, physical chemistry, and biochemistry, as well as faculty and advanced students.