Correspondence; manuscripts; notebooks; lectures; diaries; memorabilia. The bulk of the collection is correspondence, primarily incoming letters (1878-1912) with mathematicians and physicists on current work. Exchanges of particular interest include those with Sophus Lie which reveal Poincar'̌s thinking on the genesis of the axioms of geometry; Heinrich Hertz on Hertz's experiments on electromagnetic waves, and his interest in the three body problem of classical mechanics; correspondence on the Crm̌ieu controversy; discussions of theories of analytic functions, number theory, and differential equations; and papers Poincar ̌published in Mittag-Leffler's 'Acta Mathematica.' Also contains letters from Poincar ̌to his family while a student at l'Ecole Polytechnique (1873-1875) and L'Ecole des Mines (1877-1879). Manuscripts and calculations are for many of his published papers in mathematics, science, and philosophy. Notebooks and lectures (1897-1899) are for his courses at the Universit ̌de Paris. Topics include elliptical functions, complex variables, linear differential equations, n-body problems, celestial mechanics, potential theory, fluid mechanics, and wireless telegraphy. Travel diaries are from his 1878 trip to Norway and Sweden. Also contains publishing contracts; correspondence and documents pertaining to memberships and awards including Poincar'̌s election to l'Acadm̌ie francaise; and memorial clippings. Correspondents include R. Blondlot, Thomas Craig, George Howard Darwin, Charles Hermite, William Thomson (Lord Kelvin), A. Leburt, and Alfred Potier.