Originally of European origin, the Harmonium (peti, or Baja) began to be implemented into Indian music during the 19th century. The overall shape of the instrument is that of a box. Running along the top of the box is a row of keys, or chabi, similar to that of a piano. An instrument without a keyboard but similar to a harmonium is called a surpeti & is used to generate an underlying drone. Inside the harmonium is a flat wooden reed board with several holes, although there are styles where the board is not flat. The instrument can have up to three banks of reeds, in which case it is called a triple-reed harmonium. Reeds of brass cover these holes. The reeds vibrate air passes over them, & this air is forced through the instrument when the musician pumps the bellows. The eternal bellows, which acts as a reservoir for the air pushing against a spring & forcing the air over the reeds. The control of the airflow through various reed chambers is managed by main stops. Drone stops control the flow of the air over the unkeyed reeds.

Today, it is used in virtually every music genre be it bhajan, film music, folk music, ghazal, geet, Kathak dance, qawwali, kirtan/dhun, shabad, khayal etc. Infact vocal music without harmonium cannot be even thought of. Many 19th century composers wrote serious music for the harmonium.