The mechanism of the reaction of alkylation of aromatic compounds according to Friedel–Crafts is considered. Unlike the acylation reaction, alkylation is a reversible process. The general principle of the reaction is the intermediate formation of carbenium ions capable of reacting as an electrophile in the aromatic reactions of electrophilic substitution. It is established that the mechanism of this reaction is ensured by the detection of the σ–complex at low temperatures. The possibility of using the intramolecular variant of Friedel–Crafts alkylation is considered; limitations of the applicability of the reaction as a whole are noted.