Language, coffee, and migration on an Andean-Amazonian frontier provides compelling insights into language and political economy in southern Peru's Alto Urubamba Valley. Based on nineteen months of ethnographic fieldwork (2009–2012) in a dynamic contact zone, Emlen illustrates how choices about using Matsigenka, Quechua, and Spanish are linked to interactional demands and social roles embedded in the coffee production process. Through scholarly interventions in historical linguistics, South American studies, and linguistic anthropology, Emlen traces how the social identities and language practices of indigenous Matsigenka and Andean colonos have been ideologically constructed as ethnically distinct, complicating these categorical understandings by detailing the circulation of people in the region across centuries. Emlen vividly outlines these dynamics of linguistic and socioeconomic change in Yokiri, the book's focal community, through deep analysis of the coffee production process.

In Yokiri, residents grapple with two competing desires: integration into a growing agricultural industry or isolated protection from its rapid expansion. These tensions are linked to shifting interethnic divisions and intimacies among the indigenous Matsigenka and the Andean colonos, given Yokiri's status as a protected comunidad nativa and the country's Spanish colonial history. Within this social context, Emlen analyzes three communicative processes that illustrate the interactional and ideological aspects of coffee production: speaking as a farmer, speaking as a comunero, and speaking about the land.

As community members become coffee farmers, they are socialized into complex technical registers of Spanish used to provide information about coffee cultivation during training workshops. Meanwhile, negotiations about logistics, pricing, and exchange frequently occur in Quechua through interactional strategies such as joking and persuasion. Socioeconomic inequalities are often reproduced in both spaces, as Quechua-speaking rural Andeans typically have more experience with technical Spanish registers and are also more familiar with the locally valued Quechua discursive practices of bargaining. Yet interactional spaces in Matsigenka, such as the Radio Quillabamba broadcast, provided a multilingual platform (e.g. using mock Quechua) to distribute messages between farmers and merchants and highlight issues relevant to comunidades nativas.

As the frontier expanded through coffee production, speaking as a comunero (member of the comunidad nativa) played an important role in mediating land disputes. In Asamblea meetings, Matsigenka used Spanish for official discourse to distinguish public from private interests and invoke community-level sacrifices rather than traditional kin-based commitments. In these meetings, Quechua was largely excluded given its status as a colonizing language and Matsigenka used infrequently given uneven proficiency across attendees for full participation. Finally, Emlen argues that etymological discourses about the land are not linked to specific ethnic identities but rather are used for interactional purposes to highlight ancestral, historical, and contemporary concerns. Ultimately, this book provides a rich ethnographic account of multilingual dynamics and socioeconomic change in an Andean-Amazonian frontier community, showing how language and social identity are deeply embedded in both the tensions and intimacies that are constructed through societal transformation.