Resonance Raman labels are small chromophoric molecules that are placed at biological sites as resonance Raman reporter groups. The label may resemble closely a natural biological component, or it may have no biological counterpart and be placed at the site simply to probe the properties of that site. Most of the early work with resonance Raman labels involved ligands binding to proteins, for example chromophoric substrates or inhibitors binding to enzyme active sites. The sensitivity of Raman instrumentation has increased greatly in recent years such that it no longer necessary to use the resonance condition to obtain the Raman spectrum of a ligand binding to a macromolecule. These data can now be obtained from non-resonance spectra by Raman di β erence spectroscopy. It is still advantageous if the ligand is a strong Raman scatterer and then the label becomes simply a Raman label. The advantages and disadvantages of resonance and non-resonance labels are discussed. For the latter, critical advantages of operating under non-resonance conditions and using deep red excitation are that problems associated with photochemistry and Γuorescence interference are avoided ; consequently a wide range of biochemical systems become accessible to Raman analysis.