During many decades of national isolation, a mathematical tradition called wasan flourished in Japan independently of the advances of Enlightenment mathematics and virtually unknown to Europeans before the Meiji Restoration. Yet the brilliance of its practitioners, the wasanka, would surely have been admired by Leibniz or Euler had they been able to read their solutions to often difficult geometry problems. This interpretive translation of a suite of twenty-six related problems analyzed by Aida Yasuaki (1747–1817) gives readers unfamiliar with the premodern Japanese language access to a real wasan text. Instead of presenting and solving problems using modern techniques, Unger presents Aida’s own solutions, transcribing his calculations into familiar mathematical notation, highlighting connections between Aida’s work and both the mathematics of today and aspects of Japanese cultural history. A specialist in the history of the Japanese language, he aims to bring fellow amateur mathematicians and interested professionals into contact with actual wasan methods, and to initiate a discussion of how wasan fits into the larger picture of premodern Japanese history.