This book describes the events and circumstances connected with the discovery of the electron paramagnetic resonance by Zavoisky and his colleagues. The initial successful observation of the electron paramagnetic resonance in solids and liquids was performed in 1944 at the Kazan University in Russia. It was one of the most important discoveries in physics that gave a powerful and sophisticated method to investigate substance at the atomic level, and having significant applications in chemistry, biology, medicine, geology, and many other fields.