This is a new annotated edition of Thomas J. Stieltjes' , first published in 1914 (Vol. I) and 1918 (Vol. II) by Noordhoff, Groningen, in French, and now published by Springer-Verlag, originally to mark the occasion of the 100th anniversary of Stieltjes' death (1894). These two volumes will be of great interest to all mathematicians who are anxious to understand the impact of Stieltjes' work on modern mathematics, and in particular on the theory of orthogonal polynomials and continued fractions. In addition to the reproduction of Stieltjes' papers (I–XLVII), Volume I includes about 75 pages of commentaries by contemporary mathematicians on Stieltjes' work. Volume II contains Stieltjes' papers XLVIII–LXXXIV together with English translations of his main paper "Recherches sur les fractions continues" and his short note regarding the Riemann hypothesis. A Bibliography of Stieltjes' papers is included in both volumes for the convenience of the reader.