A harmonium, also known as a reed organ or pump organ, is a keyboard instrument that produces sound by blowing air through reeds, which are tuned to different pitches to make musical notes. It can be played using either the feet or the hands, depending on the type of harmonium. The instrument was first designed by Christian Gottlieb Kratzenstein, a professor of physiology at the University of Copenhagen in the 1700s, and was inspired by the Chinese mouth organ, or sheng. The harmonium was brought to India in the late 19th century, where it became an integral part of Indian music, used to accompany folk, classical, Sufi, and ghazal compositions for both music and dance.

The harmonium has three octaves, mandra, madhya, and tara, on which twelve semitones of the tempered scale are fixed once and for all. However, it is limited in its ability to play grace notes, quarter-tones, and other essential elements of Hindustani music. For this reason, the harmonium was banned in music broadcasts over the National network in India from 1 March 1940. Despite this, the harmonium remains a popular instrument in many genres of Indian, Pakistani, and Bangladeshi music, including North Indian classical music and Sufi Muslim Qawwali concerts.