Vulgar Latin, also known as Popular or Colloquial Latin, is the range of non-formal registers of Latin spoken from the Late Roman Republic onward. Vulgar Latin as a term is both controversial and imprecise. Spoken Latin existed for a long time and in many places. Scholars have differed in opinion as to the extent of the differences, and whether Vulgar Latin was in some sense a different language. This was developed as a theory in the nineteenth century by Raynouard. At its extreme, the theory suggested that the written register formed an elite language distinct from common speech, but this is now rejected.

Latin is a classical language belonging to the Italic branch of the Indo-European languages. Considered a dead language, Latin was originally spoken in Latium, the lower Tiber area around Rome. Through the expansion of the Roman Republic it became the dominant language in the Italian Peninsula and subsequently throughout the Roman Empire. Even after the fall of Western Rome, Latin remained the common language of international communication, science, scholarship and academia in Europe until well into the early 19th century, when regional vernaculars supplanted it in common academic and political usage—including its own descendants, the Romance languages. For most of the time it was used, it would be considered a dead language in the modern linguistic definition; that is, it lacked native speakers, despite being used extensively and actively.