| Arthur von Oettingen | |
| Birth Place: | Ludenhof Manor, Ludenhof, Kreis Dorpat, Governorate of Livonia, Russian Empire (present-day Luua, Tartu County, Estonia) |
| Death Place: | Bensheim, Kreis Bensheim, Province of Starkenburg, Hesse, Weimar Republic |
| Resting Place: | Südfriedhof (Leipzig) |
| Nationality: | Baltic German |
| Fields: | Physics, musical theory |
| Academic Advisors: | Antoine César Becquerel, Henri Victor Régnault, Heinrich Gustav Magnus, Johann Christian Poggendorff, Heinrich Wilhelm Dove |
| Known For: | Introducing the harmonic dualism and millioctave concept |
| Relatives: | Alexander von Oettingen (brother) Georg von Oettingen (brother) |
Arthur Joachim von Oettingen (– 5 September 1920) was a Baltic German physicist and music theorist. He was the brother of theologian Alexander von Oettingen (1827–1905) and ophthalmologist Georg von Oettingen (1824–1916).
He studied astronomy and physics at the University of Dorpat, and furthered his education of physics in Paris in the laboratories of Antoine César Becquerel (1788–1878) and Henri Victor Régnault (1810–1878), and afterwards at Berlin in the laboratories of Heinrich Gustav Magnus (1802–1870), Johann Christian Poggendorff (1796–1877) and Heinrich Wilhelm Dove (1803–1879).
In 1868 he became a professor at Dorpat, where he founded a meteorological observatory. In 1893 he moved to the University of Leipzig, where he remained until 1919 as a teacher and honorary professor. In 1898 and 1904 he published the third and fourth volumes of Poggendorff's Biographisch-Literarisches Handwörterbuch der exakten Naturwissenschaften.
Oettingen was a primary advocate of a theory of acoustical relationships known as "harmonic dualism". This concept was later expanded and elaborated on by musicologist Hugo Riemann (1849–1919). Oettingen is also credited for introducing a measurement of musical interval known as the millioctave. He later created a musical instrument, the Orthotonophonium - a pump organ using 72 notes per octave, to further advocate harmonic dualism.