Music listening can evoke a range of extra-musical thoughts, from colors and smells to autobiographical memories and fictional stories. We investigated music-evoked thoughts as an overarching category, to examine how the music’s genre and emotional expression, as well as familiarity with the style and liking of individual excerpts, predicted the occurrence, type, novelty, and valence of thoughts. We selected 24 unfamiliar, instrumental music excerpts evenly distributed across three genres (classical, electronic, pop/rock) and two levels of expressed valence (positive, negative) and arousal (high, low). UK participants (N = 148, Mage = 28.68) heard these 30-second excerpts, described any thoughts that had occurred while listening, and rated various features of the thoughts and music. The occurrence and type of thoughts varied across genres, with classical and electronic excerpts evoking more thoughts than pop/rock excerpts. Classical excerpts evoked more music-related thoughts, fictional stories, and media-related memories, while electronic music evoked more abstract visual images than the other genres. Positively valenced music and more liked excerpts elicited more positive thought content. Liking and familiarity with a style also increased thought occurrence, while familiarity decreased the novelty of thought content. These findings have key implications for understanding how music impacts imagination and creative processes.