Usul may refer to:
Islam From ( of "root", "principle"): Usul al-fiqh, the principles of Islamic jurisprudence Usul al-din, the principles of Islamic religion
Books Usul al-Sama, a Sunny treatise Usul al-Ifta wa Adabuhu, a Fiqh guide
Music Usul (music), a rhythmic pattern used in Ottoman classical music.
Characters Usul, the secret tribal name of Paul Atreides in Frank Herbert's Dune novels a species in Neopets