Louis de Cahusac (6 April 1706 – 22 June 1759) was an 18th-century French playwright and librettist, and Freemason, most famous for his work with the composer Jean-Philippe Rameau.
He provided the libretti for several of Rameau's operas, namely Les fêtes de l'Hymen et de l'Amour (1747), Zaïs (1748), Naïs (1749), Zoroastre (1749; revised 1756), La naissance d'Osiris (1754), and Anacréon (the first of Rameau's operas by that name, 1754).
He is also credited with writing the libretto of Rameau's final work, Les Boréades (c.
Cahusac contributed to the Encyclopédie and was the lover of Marie Fel.In 1754, he published La Danse ancienne et moderne ou Traité historique de la danse (The Hague, Jean Neaulme).
Among Rameau's librettists, he was the one whose collaboration lasted the longest; the composer was having a very bad character and he was also very stingy: only Cahusac managed to agree with him permanently.