Hydrogen bond (HB) between water and organic molecules plays dominant roles for the properties of a large number of organic solutions. Although the IUPAC has defined the HB (X δ--H δ+ ⋅⋅⋅Y δ-) to feature the intermolecular interactions involving the protons and electron lone pairs, the HB is often referred to the H⋅⋅⋅Y attraction. In the HB, X and Y have a higher electronegativity than H, and therefore X and Y, such as C, N, O, and F, carrying negative charges. The X is referred to as the donor, and the Y as the acceptor of proton H; "-" represents a covalent bond between the X and H, while the "⋅⋅⋅" represents a nonbond interaction between H and Y. The IUPAC's definition has advanced the properties design and utilization of water and organic crystals which involve the HB.