NMR spectroscopy is a powerful technique for determining the structures of molecules in solution. It involves placing a sample in a strong homogeneous magnetic field and irradiating it with radiowaves of defined frequency. The emitted signals provide information about the local molecular environments of nuclei in the sample, from which structures can be derived. NMR can also be used for determining interactions between molecules and is particularly useful for determining the nature of binding interactions between ligands and macromolecules. This information is very important in drug design: by understanding how bioactive molecules interact with a target protein or nucleic acid it is, in principle, possible to design ligands with improved affinity and specificity that may make useful drug leads. In addition to this structure‐based approach to drug design NMR is also useful as a screening tool in drug discovery programs to identify ligands that bind to target macromolecules.