《L.H.O.O.Q.》（法语发音：[el aʃ o o ky]），或译带胡须的蒙娜丽莎，是杜象一系列依据《蒙娜丽莎》改造而成的作品，最早的一幅完成于1919年，属于“现成品”（Readymades）艺术。最初杜象只是给达芬奇的这幅画作上的人物用铅笔加了两撇小胡子，然后重命名为L.H.O.O.Q.而已。 实际上法国画家欧仁·巴代伊（Eugène Bataille）在1883年就创作过类似的作品，那次是给蒙娜丽莎加上了一个烟斗。通常评论家都把这幅画看作是对传统艺术的嘲讽。

L.H.O.O.Q. (French pronunciation: ​[ɛl aʃ o o ky]) is a work of art by Marcel Duchamp. First conceived in 1919, the work is one of what Duchamp referred to as readymades, or more specifically an assisted ready-made. The readymade involves taking mundane, often utilitarian objects not generally considered to be art and transforming them, by adding to them, changing them, or (as in the case of his most famous work Fountain) simply renaming them and placing them in a gallery setting. In L.H.O.O.Q. the objet trouvé ("found object") is a cheap postcard reproduction of Leonardo da Vinci's Mona Lisa onto which Duchamp drew a moustache and beard in pencil and appended the title.