British mathematician, logician and philosopher best known for his work in mathematical logic and the philosophy of science. In collaboration with Bertrand Russell, he authored the landmark three-volume Principia Mathematica (1910, 1912, 1913) and contributed significantly to twentieth-century logic and metaphysics. Although there are important continuities throughout his career, Whitehead's intellectual life is often divided into three main periods. The first corresponds roughly with 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, covering the years from 1910 to 1924, corresponds with his time at London. During these years Whitehead concentrated mainly, but not exclusively, on issues in the philosophy of science and the philosophy of education. The third main period corresponds roughly with his time at Harvard, from 1924 onward. It was during this time that he worked on more general issues in philosophy, including the development of a comprehensive metaphysical system which has come to be known as process philosophy.