Medieval Latin refers to the Latin used in the Middle Ages, after the fall of the Roman empire but before the rise of vernacular languages in the Renaissance. It is largely synonymous with Church Latin.

Medieval Latin was characterised by an enlarged vocabulary, which freely borrowed from other sources. Prominent among those sources were Greek, from which much of the technical vocabulary of Christianity came. 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 as such 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. Latin was also spread to areas such as Ireland and Germany, where Romance languages were not spoken and which had never known Roman rule. Works written in these lands where Latin was a learned language with no relation to the local vernacular also influenced medieval Latin's vocabulary and syntax.

The influence of Vulgar Latin was also apparent in the syntax of some Medieval Latin writers, although Classical Latin continued to be held in high esteem and studied as models for literary compositions. The high point of development of medieval Latin as a literary language came with the Carolingian renaissance, a rebirth of learning kindled under the patronage of Charlemagne, king of the Franks. Alcuin was Charlemagne's Latin secretary and an important writer in his own right; his influence led to a rebirth of Latin literature and learning after the depressed period colloquially known as the Dark Ages.

Although it was simultaneously developing into the Romance languages, Latin itself remained very conservative, as it was no longer a native language and there were many ancient and medieval grammar books to give one standard form. On the other hand, strictly speaking there was no single form of "Medieval Latin." Every Latin author in the medieval period spoke Latin as a second language, to varying degrees of fluency, and syntax and grammar often depended on an author's native language. Whereas Latin had no definite or indefinite articles, medieval writers sometimes used forms of unus as an indefinite article, and forms of ille (reflecting usage in the Romance languages) or even "quidam" (meaning "a certain one/thing" in Classical Latin) as something like a definite article. Unlike in classical Latin, where esse ("to be") was used as the only auxiliary verb, Medieval Latin writers might use habere ("to have"), as Germanic and Romance languages do.

The most striking differences between Classical and medieval Latin are found in orthography. Some of the most frequently-occurring differences are:

• the diphthong ae might be collapsed and written as simply e; for example, puellae might be written puelle.
• h might be lost, so that habere becomes abere, or mihi becomes mi (the latter also occurred in Classical Latin); or, mihi may be written michi, indicating the h came to be pronounced as k, which is its pronunciation even today in Ecclesiastical Latin (this pronunciation is not found in Classical Latin).
• The loss of h in pronunciation also led to the addition of h in writing where it did not previously belong, especially in the vicinity of r, such as chorona for corona, a tendency also sometimes seen in Classical Latin.
• t might be written as c, especially between vowels, so that divitiae becomes diviciae (or divicie)
• mn, mt, and other nasal+plosive combinations might have another plosive inserted between them, so that alumnus becomes alumpnus.
• single consonants were often doubled, or vice versa, so that tranquillitas becomes tranquilitas.
• vi, especially in verbs in the perfect tense, might be lost, so that novisse becomes nosse (this occurred in Classical Latin as well but was more frequent in Medieval Latin).

These orthographical differences were often due to changes in pronunciation, which authors reflected in their writing. By the 16th century, Erasmus complained that speakers from different countries were unable to understand each others' Latin.

Important medieval Latin authors

• Pierre Abélard
• Aetheria
• Albertus Magnus
• St Thomas Aquinas
• The Archpoet
• Bede
• Geoffrey of Monmouth
• Gildas
• Gregory of Tours
• St Isidore of Seville
• St Jerome
• Peter of Blois
• Petrarch
• Thomas of Celæno
• Venantius Fortunatus
• Walter of Châtillon

Medieval Latin literary movements

• Goliards
• Hiberno-Latin

Important medieval Latin works

• Carmina Burana
• Vulgate
• Pange Lingua
• Summa Theologica
• Etymologiæ
• Dies Iræ