The wider ramifications of questions of transmission and reconstruction led Rehding to an engagement with musical media, including notation and recording technology. In particular Rehding brings German media theory (Friedrich Kittler, , Wolfgang Ernst) to bear on music theory. The mechanical siren—an unlikely musical instrument—has played an important part in shaping Rehding’s thinking about sound media, as has the little-known music theorist Friedrich Wilhelm Opelt. Much of Rehding’s work foregrounds the role of musical instruments in theorizing. He proposes that we regard them as media—promoting and inhibiting certain kinds of sounding data—that allow theorists to make certain insights. This intersection with Critical Organology, History of Science, and Thing theory is explored in a number of works. His monograph on Beethoven’s Ninth Symphony doubles as an exploration of media theory. It proposes an anti-chronological approach that re-hears this central work of the musical canon through its digital reimagination in Leif Inge’s 9 Beet Stretch (2002). Rehding has collaborated on the topic of neuroaesthetics with his husband Bevil Conway, a neuroscientist and visual artist. Rehding has published numerous articles on nineteenth- and twentieth-century music, on such composers as Ludwig van Beethoven, Richard Wagner, Franz Liszt, Igor Stravinsky and Arnold Schoenberg. His monograph "Music and Monumentality" was the first book-length exploration of this concept, exploring the imaginary connection between “big” sounds and ambitions of greatness in the music of nineteenth-century Germany. In a six vignettes, it approaches the “monumental” works of the German symphonic tradition between Beethoven and Bruckner, lodged between the aesthetics of the sublime and a nationally framed memory culture. The book has also been influential on the new field of arrangement studies. He is series editor (with David Irving) of the multi-volume Cultural History of Music for Bloomsbury. Rehding may have inadvertently coined the term “Ecomusicology” when he used this title for a review article published in 2002. Explorations of the concept of nature have been an important part of his work in the history of music theory. His more recent contributions to this field have focused increasingly on contemporary ecological concerns (apocalyptic thinking, Anthropocene, the "Long Now”). Rehding argues that music, with its flexible temporalities, has an important role to play in fostering thinking about the distant future, corresponding to one major strand of contemporary ecological thought.