This article examines the causes and variation of language standardization across European ethnic groups from a historical perspective. Although language has long garnered interest in the study of ethnicity and nationalism, how language becomes standardized has yet to be offered. In this article, I argue that the acquisition of the printing press is critical to explaining the occurrence and variation of standardization. Using the first publication of vernacular dictionaries as a proxy for standardization, I present a systematic investigation of the standardization process for 171 ethnic groups in Europe from 1400–2000 ce. Empirical tests come from an original data set that collects information on political, economic, and social dimensions. Findings from event history models show that (1) printing press adoption is positively and significantly correlated with vernacular dictionaries; and (2) early adopters are more likely to standardize vernaculars than latecomers.