Hydrogen bonding plays an essential role in maintaining the structures and thus the functions of biological macromolecules, such as nucleic acids and proteins. Recently, scalar nuclear spin couplings (J couplings) across hydrogen bonds have been observed for various hydrogen bond pairs, such as N-H…N in nucleic acids and N-H…O=C in proteins. The coupling values range from 0.8 to 10Hz, depending on the systems and the interacting nuclei. As scalar couplings are known to be dominated by the Fermi contact term, these values can, in principle, be correlated to the nature of the hydrogen bonds.