In music, Op. 100 stands for Opus number 100. Compositions that are assigned this number include:
Brahms – Violin Sonata No. 2 Dvořák – Violin Sonatina Prokofiev - Symphony No. 5 Reger – Variations and Fugue on a Theme by Hiller Schubert – Piano Trio No. 2 Schumann – The Bride of Messina Sibelius – , for small orchestra (1922)