This book is the first musical, cultural, and technological history of loudness, highlighting how loudness calls attention to musical, discursive, affective, and technological continuities across seemingly disparate traditions. It explores the role of dynamics in music theory, the problematic status of the decibel in the acoustic sciences, debates about orchestration technique, and criticism in jazz, rock, and disco. Examining how loudness inflects issues in music studies including taste, race, gender, and youth, it charts an interdisciplinary path forward, highlighting the insights gained when popular music is studied alongside various forms of art music and acoustic mediation.