EPR spectroscopy 80 years after its discovery.

Electron paramagnetic resonance (EPR) spectroscopy has evolved into a powerful tool for studying matter containing unpaired electrons. By probing electron spin interactions with their environment and with other spins, EPR provides insight into electronic structure, local chemical environments, molecular motion, and intermolecular interactions across broad spatial and temporal scales. This review outlines the principles and methodology of continuous-wave and modern pulse EPR, emphasizing the framework for quantitative spectral interpretation. Applications range from metalloproteins and reactive radicals to functional materials and catalytic systems. Recent advances, including high-field EPR, pulse dipolar EPR for nanometer-scale distance measurements, hyperfine techniques for resolving weak nuclear interactions, and integrated computational modeling, have expanded the role of EPR in structural biology, chemistry, and materials science. Improvements in instrumentation, spin labeling, and sensitivity enhancement continue to broaden its applicability to increasingly complex and dilute systems, while ongoing developments in automation and data analysis are making EPR more accessible across the physical and life sciences.