The bodhran is an Irish frame drum ranging from 25 to 65 cm in diameter, with most drums measuring 35 to 45 cm. The sides of the drum are 9 to 20 cm deep. A goatskin head is tacked to one side (synthetic heads, or other animal skins are sometimes used). The other side is open ended for one hand to be placed against the inside of the drum head to control the pitch and timbre.
One or two crossbars, sometimes removable, may be inside the frame, but this is increasingly rare on modern instruments. Some professional modern bodhrans integrate mechanical tuning systems similar to those used on drums found in drum kits so the bodhran skins are tightened or loosened depending on the atmospheric conditions.
The bodhran is one of the most basic of drums and as such it is similar to the frame drums distributed widely across northern Africa from the Middle East, and has cognates in instruments used for Arabic music and the musical traditions of the Mediterranean region (see Music of North Africa, Music of Greece etc.). A larger form is found in the Iranian daff, which is played with the fingers in an upright position, without a stick. Traditional skin drums made by some Native Americans are very close in design to the bodhran as well.
There is a close similarity between the bodhran and Spanish military drums of previous centuries, suggesting the instrument may have been introduced by Irish who had served in the Spanish military or acquired knowledge of the instrument from Spanish comrades aboard sailing ships.
It has also been suggested that the origin of the instrument may be the skin trays used in Ireland for carrying peat; the earliest bodhran may have simply been a skin stretched across a wood frame without any means of attachment.