Institutions play an important role in the management of multilingualism and can have a defining impact on language use. By granting more or less official status to certain forms of expression and language varieties, institutions legitimize some forms and varieties as more desirable targets of linguistic accommodation than others, which can affect speakers’ dominant language environments and influence the selection process of language change. This chapter outlines a socio-political approach to language standardization and interprets selected language policy and planning measures in terms of common mechanisms and outcomes of language contact in three western European states: France, Spain, and the United Kingdom. Using the same historical timeline, it proposes a comparison of the circumstances under which national identities emerged in early modern and modern times, state boundaries were expanded through conquest, and more or less cultural homogeneity was achieved and enforced through language use. It is argued that even though ethnolinguistic diversity decreased considerably over time, different institutional responses to multilingualism led to different state-specific compromises that continue to shape language policies and planning in each of the three states today.