Medieval Latin was the form of Latin used in the Middle Ages, primarily as a medium of scholarly exchange and as the liturgical language of the medieval Roman Catholic Church, but also as a language of science, literature, law, and administration. Despite the clerical origin of many of its authors, medieval Latin should not be confused with Ecclesiastical Latin. There is no real consensus on the exact boundary where Late Latin ends and medieval Latin begins. Some scholarly surveys begin with the rise of early Ecclesiastical Latin in the middle of the 4th century, others around AD 500, and still others with the replacement of written Late Latin by written Romance languages starting around the year 900 (see under Late Latin).

Medieval Latin had an enlarged vocabulary, which freely borrowed from other sources. It was heavily influenced by the language of the Vulgate, which contained many peculiarities alien to Classical Latin that resulted from a more or less direct translation from Greek and Hebrew; these peculiarities mirrored the original not only in its vocabulary, but also in its grammar and syntax. Greek provided much of the technical vocabulary of Christianity. The various Germanic languages spoken by the Germanic tribes, who invaded western Europe, were also major sources of new words. Germanic leaders became the rulers of western Europe, and words from their languages were freely imported into the vocabulary of law. Other more ordinary words were replaced by coinages from Vulgar Latin or Germanic sources because the classical words had fallen into disuse.