Framed as part of a broader project focused on the creative process of music composers, this study aimed to investigate their perceptions of the sources of inspiration behind their music composition process. These perceptions were explored through a thematic analysis of published interviews conducted with a sample of vanguard contemporary music composers. Results of this analysis point to five general sources of inspiration for composing music, some involving specific sources of inspiration with different variations: natural world (physical/biological), human world (psychological/social), holistic world, culture (general, art/non-art), and synthesis of influences.