Leibniz's originality of mind left its mark on each of the many areas in which he was active. His detailed memoranda, covering the more than 40 years of his political career, constitute in themselves a major source for the history of this period. His contributions in the field of mathematics had forceful impact on the work of his contemporaries and immediate successors. His innovative ideas in political theory and philosophy, on the other hand, were not congenial to the thought of his times; in the 19th and 20th centuries, however, many of his theories have given rise to important developments in these and related fields, ranging from Freudian psychology to Einsteinian physics, and he is now recognized as one of the most fertile and profound intellects of the age of the Enlightenment.
Generous selections from Leibniz's writings are in Leibniz: Selections, translated by Philip P. Wiener (1951), and Gottfried Wilhelm von Leibniz: Philosophical Papers and Letters, translated with an introduction by Leroy E. Loemker (2 vols., 1969). There is no full-scale modern biography in English. John T. Merz, Leibniz, a 19th-century German biography, is available in an English translation (1948). For a general estimate of Leibniz and his work, Ruth L. Saw, Leibniz (1954), is useful, and Cornelius A. van Peursen, Leibniz (trans. 1969), is a perceptive short study. Bertrand Russell, A Critical Exposition of the Philosophy of Leibniz (1900; 2d ed. 1951), is a comprehensive interpretation. Still worth consulting is Herbert W. Carr, Leibniz (1929). For a more complete discussion of Leibniz in relation to his times than the histories of science and mathematics afford, Rudolf Meyer, Leibniz and the 17th Century Revolution (trans. 1952), is recommended.