Ronald E. Cohen is an American scientist at the Carnegie Institution for Science's Geophysical Laboratory. He is a theorist who works on understanding materials, ranging from minerals to technological materials like ferroelectrics. Much of his work has centered on materials at extreme conditions, like the high pressures at the center of the Earth, and on transducer materials, used for sonar and medical ultrasound. He is one of the pioneers for applying of first-principles methods to minerals. In first-principles methods, only the atom types are input, and all properties can be computed using quantum mechanics. He also expanded the application of these methods to ferroelectrics, and continues to clarify the origin of ferroelectric and relaxor behavior.