Hornbostel-Sachs, sometimes called Sachs-Hornbostel is the most widely used system used to classify musical instruments. It was devised by Erich Moritz von Hornbostel and Curt Sachs and published in 1914 in "Zeitschrift für Ethnologie. It was translated into English in 1961 by the Galpin Society.

This system is an expansion on a system devised by Victor-Charles Mahillion, who was the curator of The Brussels Conservatory's musical instrument collection. It is also based on the Dewey Decimal book classification system.

The Hornbostel-Sachs system has five top level classifications:

1. Idiophones, an instrument that creates sound by vibration of the instrument itself, without use of membrane or strings.
 
2. Membranophones, an instrument that creates sound by vibration of a stretched membrane.

3. Chordophones, an instrument that creates sound by vibration of a string or a string stretched between 2 points.

4. Aerophones, an instrument that creates sound by vibration of a body of air, without the use of strings or membranes, and without the vibration of the instrument itself.

5. Electrophones, an instrument which produces sound by the use of electricity. This category was officially added to the system in 1940.