While there is a large number of double reed instruments throughout musical history, in modern terms the most commonly seen and played are the oboe, cor anglais, and bassoon. Unlike clarinets which use a single reed vibrating against a mouthpiece to produce a sound, double reed instruments - as the name suggests - produce their sound by using two reeds bound together on opposite sides of a tube to make their noise. An amount of pressure is required to produce and control the sound.
In terms of ensemble music, bassoon duets, oboe duets and trios are the most common. However for a fuller sound oboes can be matched with a cor anglais which is pitched lower. Some ensemble music uses oboes with a bassoon for a bass line. Other double reed instruments include the oboe d'amore and the contra bassoon but these are rarely played in modern music.
You can find a selection of double reed ensemble sheet music on the website.