The Irish pipes, also known as "union pipes" or "uilleann pipes," are one of several small, bellows-blown bagpipes. Small pipes were first developed by the French in the latter years of the 16th century (musette de cour) to reduce the loudness of bagpipes such that their music could be enjoyed indoors. The Irish pipes are first known to have appeared in the mid-18th century, and are believed to have evolved from the pastoral pipes.
The Irish pipes include a chanter with a double-reed for playing the melody, and drone pipes for maintaining an underlying tone, against which the melody is played. The drones are typically tuned an octave apart, and are equipped with what is called a guill, or single reed. Like other bagpipes, the chanter is tuned in Just Intonation so that its notes will blend with the drones. The chanter of the Irish pipes is stopped against the players's thigh, allowing the playing of notes either "opened" (off the thigh) or "closed" (on the thigh). By building up pressure on the closed chanter, the player is also able to play up into the second and third octaves, something that few other bagpipes are capable of.
The Irish pipes first stood out from other small pipes with the addition of a second double-reed chanter called a "regulator," equipped with three or four keys that lay with the drones across the player's lap. By pressing the keys of the regulator with his wrist the player was able to add harmony notes in "union" with the chanter, leading to the popular name of "union pipes." The term "regulator" suggests some relation to terms used for reed and pipe organs, and the Irish pipes have sometimes been called the "Irish organ" in the past.
Continued development of the Irish pipes in the 19th century saw the addition of three or more regulators, making the Irish pipes the most technically complicated bagpipes in the world. Usually a full set of Irish pipes today will consist of the chanter, bag and bellows, three drones (tenor, baritone, bass) and three regulators (tenor, baritone, bass), but additional drones and/or regulators have been added or subtracted on customized sets.
Although pitch standards have changed several times since the Irish pipes were first developed, most sets in the past were pitched according to the length of the chanter, e.g. a 16-inch chanter, a 17-inch chanter, etc. Towards the second half of the 19th century, as the Irish pipes emigrated to the USA along with many of the inhabitants of Ireland, players found that the Irish pipes, so well suited to performance in the parlour, were too quiet for the concert stage and large public dances. This led to the development of a chanter with a louder design made with a wider bore. Typically, these wider bore sets were pitched in the key of D, so that wide-bore D sets came to be known as "concert sets" or "concert pitch" sets. Older sets, with their quieter, narrower bores were usually pitched lower than, or flat of, the key of D, so they became collectively known as "flat sets". Flat sets are typically pitched in C#, C, B, or B♭.
By the early 20th century the term "union pipes" was no longer considered politically correct in Ireland, and the term "uilleann" (pronounced ill-en), meaning "of the elbow," was adopted in Ireland. The terms "Irish pipes" and "uilleann pipes" are still current today.
The sound of the Irish pipes is unmistakable, and they are often heard in sound-tracks for movies and television shows as well as in concerts by Irish or "Celtic" bands, but they are heard at their best when played solo. The player can turn the drones on and off at will, can accompany himself with the regulators, and can manipulate the chanter to produce a wide range of musical and emotionally moving sounds, making the Irish pipes a very complete and satisfying instrument.