This book offers the first musical, cultural, and technological history of loudness, highlighting how loudness calls attention to musical, discursive, affective, and technological continuities that stretch across seemingly disparate traditions. Devine focuses especially on the years since 1915, when the forerunner of the modern loudspeaker was invented, and thus when loud sound became possible in new ways. The book corrects the fact that loudness remains surprisingly un-theorized and un-historicized, especially considering its longstanding importance as a source of pleasure, an object of criticism, and an engine of technological change. In exploring topics ranging from the role of dynamics in music theory to the problematic status of the decibel in the acoustic sciences, and from debates about orchestration technique to criticism in jazz, rock, and disco, the book breaks away from the generic and stylistic orthodoxies that circumscribe existing histories of twentieth-century music. Examining how loudness inflects central issues in music studies, including taste, race, gender, and youth, it argues that the crescendo model of the history of loudness stems from an impoverished understanding of music and sound as functions of their social settings. This volume charts an interdisciplinary path forward for music studies, highlighting the insights that can be gained when popular music is studied alongside various forms of art music and acoustic mediation, as overlapping phenomena in a shared history of sound and listening.