The analysis of Berezin and Kiselev’s concept assuming linear association of molecules in a localised adsorption monolayer on the homogeneous surface of a solid adsorbent was carried out. An inconsistency due to the lack of consideration of equilibrium concentration of free adsorption sites in the formulation of the expression for the association constant has been pointed out. It was shown that the correct form of this function leads to the final adsorption equation being identical to the specific case of the Fowler-Guggenheim equation. The obtained result has been generalised to cases of branched adsorbateadsorbate associations. A new adsorption equation limiting the association to at most the dimers has been introduced. Critical conditions for the two-dimensional condensation of the adsorption layer were determined. By applying the formalism of canonical ensemble, full equivalence of the phenomenological and statistical methods was demonstrated in the description of the intermolecular interactions in the localised adsorption monolayer.