Ludwig van Beethoven's Piano Sonata No. 26 in E♭ major, Op. 81a, known as Les Adieux ("The Farewell"), was written during the years 1809 and 1810.

The title Les Adieux implies a programmatic nature. The French attack on Vienna, led by Napoléon Bonaparte in 1809, forced Beethoven's patron, Archduke Rudolph, to leave the city. Yet, there is some uncertainty about this nature of the piece — or at least, about the degree to which Beethoven wished this programmatic nature should be known. He titled the three movements "Lebewohl", "Abwesenheit", and "Wiedersehen" ('farewell', 'absence', and 'reunion'), and reportedly regarded the French "Adieux" (said to whole assemblies or cities) as a poor translation of the feeling of the German "Lebewohl" (said heartfully to a single person). Indeed, Beethoven wrote the syllables "Le-be-wohl" over the first three chords.

On the first 1811 publication, a dedication was added reading "On the departure of his Imperial Highness, for the Archduke Rudolph in admiration".

An average performance of the piece lasts about 17 minutes. The sonata is one of Beethoven's most challenging sonatas because of the mature emotions that must be conveyed throughout as well as the technical difficulties involved. It is also the bridge between his middle period and his later period and is considered the third great sonata of the middle period.