Carbohydrates are the largest natural carbon source when compared to lignin, fatty acids, proteins and other biomass resources. One carbohydrate dehydration product, 5-hydroxymethylfurfural (HMF), is a versatile platform chemical used to derive a number of important C6 compounds, including 2,5-furandicarboxylic acid (FDCA), 2,5-dimethylfuran (DMF), 2,5-diformylfuran (DFF), adipic acid, caprolactone and levulinic acid. Due to structural similarity, FDCA could replace petrochemical-purified terephthalic acid (PTA) for the synthesis of bio-based polyesters to be used for the fabrication of plastic bottles, fibres and films. The oxidation product of HMF, FDCA, is among the original United States Department of Energy's top twelve value-added building blocks. HMF was not on the list because of its lack of high synthetic selectivity and yield. HMF is reactive and can undergo conversion to levulinic acid, humin and other by-products during the dehydration process. Dehydration technology of carbohydrates into HMF has improved since then; in particular, higher yields were realized in ionic liquid media. It is on the ‘Top10 + 4’ revised list of bio-based product opportunities from carbohydrates. This chapter describes the current progress on HMF formation by dehydration of carbohydrates and sugars as well as one-pot direct synthesis of HMF form lignocellulose in ionic liquids.