The latest advances in the quantitative prediction of the influence of the composition of the aqueous and organic phases, the nature of the functional groups of the extractants and the substituents attached to these groups, and the nature of the diluent on the position of extraction equilibria in the extraction of various metals are examined. The influence of these factors on the selectivity in the separation of different elements as well as elements with similar properties and on the possibility of the far reaching removal of impurities comprising weakly extractable elements from the element to be extracted is analysed and their influence on the properties of extraction systems, as determined by the interfacial tension, is estimated. It is shown that the corresponding quantitative prediction can be made with adequate accuracy for a wide range of systems on the basis of equations derived from linear free energy relations and the tabulated parameters ID, ID*, ΔG*hydr, etc., obtained by statistical treatment of the available extensive sets of extraction data, as well as the parameters σ*, σ, E*S, H, etc. known in physical organic chemistry. The ways of applying the methods for the prediction of extraction equilibria in combination with mathematical modelling to the optimisation of the structure and regimes of technological extraction schemes are considered. The bibliography includes 182 references.