The early years of the nineteenth century saw wide-ranging developments to the mechanics and acoustics of the Classical clarinet. The Russian virtuoso clarinetist, composer, and instrument designer Iwan Müller brought about some of the most important innovations in clarinet design. His “clarinet omnitonique,” a thirteen-keyed instrument, was radical in that it would be able to play comfortably in all tonalities, dispensing with the need for the family of clarinets pitched in different keys. For a prototype of this “nouvelle clarinet”—a collaboration between Müller and the noted Viennese maker, Johann Merklein—the German composer Philipp Jakob Riotte (1776–1856) wrote a virtuosic concerto. This premiered in Vienna in the autumn of 1809. Published in 1818, and previously thought to be lost, Riotte’s op. 36 for the prototype “clarinet omnitonique” displays a diverse palette of keys, extreme registral contrasts, and chromatic writing for clarinet, which were clearly facets of Müller’s playing enabled by his new instrument. The work enhances our understanding of the development and deployment of the “clarinet omnitonique” within the concerto genre in the early nineteenth century. It serves also to reinstate the important relationship between Müller, Riotte, and Merklein.