Staehelin’s study addresses the question of the authenticity of the Sinfonia Concertante in E-flat major, a work that has been attributed to Mozart. This composition was found as part of the legacy of Mozart’s biographer Jahn, and has always been identified with the work Mozart composed in 1778 in Paris, which vanished soon afterwards. The study cites new sources and analyzes the stylistic peculiarities of the work in order to show that it could not possibly be a genuine composition by Mozart.