Historically, the ANL Chemistry Division is recognized worldwide for the development of advanced EPR techniques and their application to photochemistry research. The pioneering R&D in the field of EPR carried out at ANL includes: time-resolved EPR technique, pulsed and Fourier-Transform EPR spectroscopy, discovery of the spin-correlated phenomenon in radical pairs, basic principles of spin chemistry, RYDMR and ENDOR of natural and artificial photosynthetic systems. This work was accomplished by former ANL staff scientists including: G. Closs, M. Thurnauer, J. Norris, M. Bowman, A. Trifunac, J. Tang, M. Wasielewski, and M. Forbes. These traditions continue to be carried out by O. Poluektov, a pioneer in the field of high-resolution, high-frequency EPR spectroscopy. The development of high-frequency EPR has led to breakthroughs in many scientific fields, including photosynthesis.