Hornbostel–Sachs (or Sachs–Hornbostel) is a system of musical instrument classification devised by Erich Moritz von Hornbostel and Curt Sachs, and first published in the Zeitschrift für Ethnologie in 1914. An English translation was published in the Galpin Society Journal in 1961. It is the most widely used system for classifying musical instruments by ethnomusicologists and organologists (people who study musical instruments).
Hornbostel and Sachs based their ideas on a system devised in the late 19th century by Victor-Charles Mahillon, the curator of musical instruments at Brussels Conservatory. Mahillon divided instruments into four broad categories according to the nature of the sound-producing material: air column; string; membrane; and the body of the instrument. However, these categories were not new; they derive from the Natya Sastra, a roughly two-thousand-year-old Indian theoretical treatise on music and dramaturgy. Mahillon limited his system, for the most part, to instruments used in European classical music. From this basis, Hornbostel and Sachs expanded Mahillon's system to make it possible to classify any instrument from any culture.
Formally, the Sachs–Hornbostel is modeled on the Dewey Decimal Classification for libraries. It has four top-level classifications, with several levels below those, adding up to over 300 basic categories in all. The top three levels of the scheme are described below.