 Although there are important continuities throughout his career, Whitehead’s intellectual life is often divided into three main periods. The first corresponds roughly to his time at Cambridge from 1884 to 1910. It was during these years that he worked primarily on issues in mathematics and logic. It was also during this time that he collaborated with Russell. The second main period, from 1910 to 1924, corresponds roughly to his time at London. During these years Whitehead concentrated mainly on issues in physics, the philosophy of science, and the philosophy of education. The third main period corresponds roughly to his time at Harvard from 1924 onward. It was during this time that he worked primarily on issues in metaphysics.