Early modern London was multilingual, and early modern urban life was shaped by linguistic diversity. This article draws on the multilingual archives of Elizabethan London's ‘stranger churches’ – Protestant congregations which catered to the needs of French-, Dutch- and Italian-speaking migrants (among others) – to explore how linguistic diversity shaped social relations. These sources offer insights into the everyday multilingualism of the early modern city. They demonstrate London's migrant communities’ intense interest in what people said and why, and show how different languages and their speakers interacted on the streets and in the spaces of later sixteenth-century London. By charting how linguistic diversity was part of the lives of ordinary Londoners in this period, including close examination of incidents of multilingual insult, slander, and conflict, this article argues that the civic and religious authorities relied on the stranger churches’ abilities to carry out surveillance of speech in languages other than English, and that urban social relations and urban spaces were shaped by multilingualism. It ends by arguing that linguistic diversity played an essential but understudied role in the social history of early modern cities.