Publisher Summary The pyrylium salts represent one of the fundamental heterocyclic systems and are the basis of important natural products such as the anthoeyanins. This chapter reviews the scope, nomenclature, formulation, and syntheses of pyrylium salts. The syntheses of pyrylium salts are classified into three groups, according to the number of building blocks required to form the ring in a one-step process. The three groups are: (1) one-component syntheses, (2) two-component syntheses, and (3) three-component syntheses. Pyrylium salts bearing aromatic or heterocyclic substituents, or possessing fused saturated rings and considered as monocyclic pyrylium salts are discussed. A number of reactions starting from pyrylium salts and involving substitution at the pyrylium ring, or modification of existing substituents are also described. Pyrylium salts are useful intermediates in the conversion of aliphatic starting materials into aromatic carbocyclic or heterocyclic compounds. Some practical applications of pyrylium salts emerged are: fluorescent dyes, photosensitizers for silver halides, or photographic emulsions.