Surface plasmon resonance (SPR) spectroscopy is a real-time, optical technique that has gained widespread use in surface science and biomolecular interaction analysis since the early 1990s. In SPR experiments, molecules of interest are immobilized on a solid substrate, and their interaction with ligands is monitored to elicit information such as the binding affinity. The SPR data—reflectivity spectra or sensorgrams—can be used to determine bulk concentration and rate constants, as well as to extract parameters on binding energy, recognition sites, interaction mechanisms, and stoichiometry. The key advantage of SPR spectroscopy over conventional fluorescence or radiological assays in biomolecular interaction analysis is that no labeling is required. Although fluorescent labels allow high detection sensitivity, they have the drawback of potentially altering the native state of the studied species, particularly in proteins and peptides.