<p>The state of molecular modeling of surface and small systems is discussed. Of key importance for them is the notion of the existence of laminating phases by analogy with macrophases, although small systems themselves are not, strictly speaking, phases, and the methods of their calculation should be controlled by strict approaches of statistical physics corresponding to equilibrium states. They include the Yang–Lee condensation theory (Lee–Yang theory of phase transitions) which excludes the parameters of metastable regions inside the separation curves for a volume phase and also exact solutions in discrete lattice models in the vicinity of critical points. The discussion concerns a uniform approach towards the formation of two-phase systems in complex porous systems based on the Yang–Lee theory about the exclusions of metastable states. This principle is discernible on the examples of liquid droplets in the vapor phase, for two-dimensional systems, and in the formation of two-phase states inside porous systems, including the discussion of results on the correctness of using the Kelvin equation.</p>