The pipe organ is a musical instrument that produces sound by forcing pressurized air (referred to as wind) through a series of pipes. The size of pipe organs varies greatly: the smallest portable organs may have only a few dozen pipes, while the largest organs may feature tens of thousands.
Organ pipes sound when a key is depressed on a keyboard, allowing the wind to pass through one or more pipes from a chest beneath them. Modern organs usually include more than one keyboard playable by the hands and one keyboard playable by the feet. Large organs commonly have four or five keyboards, and a few of the very largest have six or seven.
Because of its continuous supply of wind the organ is capable of sustaining sound for as long as a key is depressed, unlike other keyboard instruments such as the piano and harpsichord, whose sound begins to decay immediately after the key is struck.
The pipe organ has been described as one of the oldest musical instruments—its origins can be traced back to Ancient Greece in the third century BC. The wind supply was originally created with water pressure (hence the name "water organ"); later, the wind was supplied from bellows. Early portable organs were used to accompany both sacred and secular music.
During the Renaissance, the organ developed from these simple forms toward a complex instrument capable of producing several different timbres, and by the end of the seventeenth century, the organ was recognisably akin to the instruments we see today.
Pipe organs are found in churches and synagogues, as well as secular town halls and arts buildings, where they are used in the performance of classical music. The organ boasts a substantial repertoire of both sacred and secular music spanning a period of more than 400 years.