The structure of the layered alpha(1)-VOPO4, VOPO(4)2 H2O, and their intercalation reactions are discussed. These reactions are divided into two groups. The first includes intercalation reactions of molecular guests which proceed as acid-base processes between the host layered lattice (Lewis acid) and a donor atom of the guest (base). Interaction of water molecules, alcohols, amines, carboxylic acids and their derivatives, heterocyclic N- and S-donors, and complex compounds with vanadyl phosphates is discussed. Vanadyl phosphate, in particular vanadyl phosphate dihydrate can also undergo the second type of the reactions which involves the reduction of a fraction of vanadium(V) atoms to vanadium(IV) with concomitant intercalation of alkylammonium, hydronium or mono-and divalent metal cations to counterbalance the induced negative layer charge. A review with 76 references.