Publisher Summary This chapter examines the formation and metabolism of di-D-fructose dianhydrides by microorganisms, and the formation of dihexulose dianhydrides by protonic and thermal activation. Dihexulose dianhydrides are intermolecular cyclic acetals formed by the condensation of two hexulose molecules with the elimination of two water molecules and the formation of two linkages involving the 2- and one other position of each component. A mechanism was proposed for the formation of di-D-fructose dianhydrides from inulin and fructose. It was suggested that α-D-Fruf-1,2ʹ :2, 1ʹ-β-D-Fruf formed first and then isomerized through ionic intermediates to produce the remaining products. Anhydrous HF has been used to produce mixed dianhydrides of D-fructose and D- or L-sorbose. The formation of these compounds was used to illustrate steric and electronic effects in the formation of dihexulose dianhydrides. It is found that the treatment of sucrose with anhydrous Hydrogen fluoride (HF) results in the formation of a complex mixture of pseudooligo- and polysaccharides up to dp 14, which was detected by fast-atom-bombardment mass spectrometry. The thermal treatment of 6-O-α-D-glucopyranosyl-D-fructofuranose (palatinose) in the presence of citric acid has been shown to produce appreciable proportions of glucosylated di-D-fructose dianhydrides.