The uilleann pipes are the characteristic national bagpipe of Ireland. Earlier known in English as "union pipes", their current name is a partial translation of the Irish language terms píobaí uilleann (literally, "pipes of the elbow"), from their method of inflation. There is no historical record of the name or use of the term uilleann pipes before the 20th century. It was an invention of Grattan Flood and the name stuck. People mistook the term 'union' to refer to the 1800 Act of Union; this is incorrect as Breandán Breathnach points out that a poem published in 1796 uses the term 'union'.
The bag of the uilleann pipes is inflated by means of a small set of bellows strapped around the waist and the right arm (in the case of a right-handed player; in the case of a left-handed player the location and orientation of all components are reversed). The bellows not only relieve the player from the effort needed to blow into a bag to maintain pressure, they also allow relatively dry air to power the reeds, reducing the adverse effects of moisture on tuning and longevity. Some pipers can converse or sing while playing. The bag which the bellows fill is clamped under the other elbow, which squeezes the bag to control the flow of air to the reeds (which make the notes).
The air goes from the bag to the chanter, drones, and regulators. The chanter is played with the fingers like a flute. The chanter has a range of two full octaves, including sharps and flats (because, unlike most bagpipe chanters, it can be overblown to produce the higher octave). The chanter is often played resting on the piper's thigh, closing off the bottom hole, so that air can only escape through the open tone holes. If one tone hole is closed before the next one is opened, a staccato effect can be created, because the sound stops completely when no air can escape at all. The three drones are simple open pipes; they constantly play three notes spread an octave apart. The three regulators are closed pipes. Untouched, they do not sound, but they have keys that can be opened by the piper's wrist action (or hand, if they take one hand off the chanter). Each regulator key sounds a different note when opened. The regulator keys are aligned so that several may be pressed simultaneously. These enable the piper to play simple chords, giving rhythmic and harmonic accompaniment as needed. There are also many ornaments based on multiple or single grace notes.
The tone of the uilleann pipes is unlike that of many other forms of bagpipes. They have a different harmonic structure, sounding sweeter and quieter than many other bagpipes, such as the Great Irish warpipes, Great Highland bagpipes or the Italian zampognas. The uilleann pipes are often played indoors, and are almost always played sitting down