Ronald S. Calinger. Leonhard Euler: Mathematical Genius in the Enlightenment . xvii + 669 pp., illus., apps., bibl., index. Princeton, N.J./Oxford: Princeton University Press, 2016. $55, £40.95 (cloth).Leonhard Euler. Correspondence . Edited by Franz Lemmermeyer and Martin Mattmüller. 2 parts. (Opera Omnia, 4A: Commercium Epistolicum, 4.) xiii + 1,248 pp., illus., figs., bibl., index. Basel: Springer, 2015. $458, £148.50 (cloth).