The Uilleann Pipes (roughly pronounced ill'-in) is one of several bagpipes indigenous to Ireland and comprises, in its modern form, a bag, bellows, chanter, three drones and three regulators.
The chanter and regulators are fitted with double reeds (similar in construction to an oboe reed) and the drones are fitted with single or beating reeds (similar to a clarinet reed but of a more primitive construction). The regulators and drones are mounted into a common stock and rest across the knee whilst playing. The air supply is provided by a bellows and the bag provides a reservoir of air.
In common with all bagpipes, the melody is played on the chanter and is accompanied by drones which sound continuously whilst the piper performs. The regulators provide a harmonic accompaniment to the melody and are played using the heel of the lower hand.
The chanter plays a major scale and may be overblown to extend its range to two octaves. With the addition of stopped keys to fill in accidental notes the chanter can play a fully chromatic scale.
The drones are tuned in octaves. The tenor drone is tuned to the root note of the chanter, the baritone drone sounds one octave below the tenor drone and the bass drone sounds two octaves below the tenor drone.
The regulators are stopped pipes running parallel to each other and are fitted with closed keys so that they do not normally sound. The keys are of varying lengths and arranged to fall into rows at right angles to the regulators. A simple chord sounds when a row of keys is opened.
Prior to about 1916 the Uilleann Pipes were known as Union Pipes, referring to the union of the sounds from the chanter, drones and regulators. They have also been known as Organ Pipes for much the same reason. The modern name was apparently invented by the writer Grattan Flood who, it is believed, thought that Union was a corruption of the Gaelic word for elbow (the bellows are pumped with the elbow), and proposed the name Uilleann to replace the "incorrect" anglicised name. Whether Flood was correct in his suppositions or not, the name has certainly proved popular and is now the accepted name for the instrument.