Dehydration of hexoses (from cellulose or hemicelluses present in lignocellulosic materials) leads to the formation of hydroxymethylfurfural (HMF), a product of growing importance that can be used as an intermediate for replacing products currently manufactured from petroleum. The development of environmentally friendly saccharification-dehydration processes applicable to lignocellulosic materials (which contain hemicellulosic polysaccharides and cellulose) fits in the scope of the “green chemistry”. For example, HMF can be reacted (in media containing acidic solutions, mixtures of water and solvents, or ionic liquids) to yield levulinic and formic acids. Levulinic acid can be used in the production of renewable polymers, the synthesis of resins, while formic acid plays an important role in the chemical industry, with applications as cleaner agent, solvent, ensilage and feed preservatives, and in the tanning and rubber industries. On the other hand, HMF can be employed to produce a number of valuable chemicals, including methyltetrahydrofuran (with applications as a solvent or fuel additive), δ-aminolevulinic acid (a broad-spectrum herbicide) and diphenolic acid.