Latin (lingua Latīna [ˈlɪŋɡʷa laˈtiːna] or Latīnum [laˈtiːnʊ̃]) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the Roman Republic it became the dominant language in the Italian region 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 18th century, when other regional vernaculars (including its own descendants, the Romance languages) supplanted it in common academic and political usage. 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.

Latin is a highly inflected language, with three distinct genders (masculine, feminine, and neuter), six or seven noun cases (nominative, accusative, genitive, dative, ablative, and vocative), five declensions, four verb conjugations, six tenses (present, imperfect, future, perfect, pluperfect, and future perfect), three persons, three moods, two voices (passive and active), two or three aspects, and two numbers (singular and plural). The Latin alphabet is directly derived from the Etruscan and Greek alphabets.

By the late Roman Republic (75 BC), Old Latin had been standardized into Classical Latin. Vulgar Latin was the colloquial form with less prestigious variations attested in inscriptions and the works of comic playwrights Plautus and Terence and author Petronius. Late Latin is the written language from the 3rd century, and its various Vulgar Latin dialects developed in the 6th to 9th centuries into the modern Romance languages.

In Latin's usage beyond the early medieval period, it lacked native speakers. Medieval Latin was used across Western and Catholic Europe during the Middle Ages as a working and literary language from the 9th century to the Renaissance, which then developed a Classifying and purified form, called Renaissance Latin. This was the basis for New Latin which evolved during the early modern era. In these periods, while Latin was used productively, it was generally taught to be written and spoken, at least until the late seventeenth century, when spoken skills began to erode. Later, it became increasingly taught only to be read.

One form of New Latin, Ecclesiastical Latin, remains the official language of the Holy See and the Roman Rite of the Catholic Church at Vatican City. When talking about current uses of Latin, we also refer to Contemporary Latin, which has limited productive use, and is rarely spoken.

Latin has also greatly influenced the English language and historically contributed many words to the English lexicon after the Christianization of Anglo-Saxons and the Norman conquest. In particular, Latin (and Ancient Greek) roots are still used in English descriptions of theology, science disciplines (especially anatomy and taxonomy), medicine, and law.