Matthew Riley’s impressive contribution to the history of music theory and psychology explores an Enlightenment ideal of listener “attentiveness.” This ideal was discussed, or more often simply referenced, by German theorists of the last three decades of the eighteenth century. Attentiveness (Aufmerksamkeit) concerned neither reverent communion with music nor rapt attention and silent contemplation; it was neither a description of social conduct nor a presentiment of Romantic and modernist listening. Rather, it described a psychological state in which the attention, as a faculty of the mind, was voluntarily exercised. Attentiveness was rarely a goal in itself; most often, it was a means to listeners’ engagement with the ruling sentiment of the piece as it unfolded through time and was subject to changes in intensity, or gave way temporarily to subsidiary sentiments. Riley traces such visions of listening to Jean-Jacques Rousseau (chapter 2), whose concepts of melodic unity and natural simplicity provided compositional-stylistic cues for audience attentiveness. At the same time, Riley notes in passing that such ideas of unity and their relationship to the listeners’ undivided attention were already present in Germany in the 1730s in the writings of Johann Mattheson. Riley sets himself the painstaking task of elucidating what the authors of his primary sources sought to communicate in their jargon-filled and often abstract texts. Riley’s readings stay close to the terms employed by contemporary authors, giving his book the character of a foundational study rather than one that explores less immediately apparent aspects of music-theoretical discourse. Given that the sources are complex and contradictory, and that the terminology and conceptual background often unclear to modern readers, this is an appropriate and difficult task which Riley executes extremely well.