On the basis of his own and literature data, the author considers and theoretically substantiates the third route to the formation and decomposition of linear and cyclic oligo- and polysiloxanes, involving intramolecular reactions of geminal fragmentation of Si(OR)X the intermediate formation (α-elimination) of short lived silanones R 2 Si O. The latter further undergo polymerization or insert into the Si-X bonds (X=O, Cl, etc.) of trapping reagents.