The legacy of the Roman Empire has been varied and significant. The Roman Empire, built upon the legacy of other cultures, has had long-lasting influence with broad geographical reach on a great range of cultural aspects, including state institutions, law, values, religious beliefs, technological advances, engineering, and language.

This legacy survived the demise of the empire (5th century AD in the West, and 15th century AD in the East) and went on to shape other civilisations, a process which continues. Rome was the civitas (reflected in the etymology of the word "civilisation") and connected with the actual western civilisation on which subsequent cultures built is the Latin language of ancient Rome, epitomized by the Classical Latin used in Latin literature, which evolved during the Middle Ages and remains in use in the Roman Catholic Church as Ecclesiastical Latin. Vulgar Latin, the common tongue used for regular social interactions, evolved simultaneously into Romance languages that still exist today, such as Italian, French, Spanish, Portuguese, Catalan, and Romanian. Although the Western Roman Empire fell in the 5th century AD, the Eastern Roman Empire continued until its conquest by the Ottoman Empire in the 15th century AD and cemented the Greek language in many parts of the Eastern Mediterranean even after the Early Muslim conquests of the 7th century AD. Roman paganism was largely displaced by Roman Catholic Christianity after the 4th century AD and the Christian conversion of Roman emperor Constantine I (r. 306–337 AD). The Christian faith of the late Roman Empire continued to evolve during the Middle Ages and remains a major facet of the religion and the psyche of the modern Western world.

Ancient Roman architecture, largely indebted to ancient Greek architecture of the Hellenistic period, has influenced the architecture of the Western world, particularly during the Italian Renaissance of the 15th century. Roman law and republican politics (from the age of the Roman Republic) have left an enduring legacy, influencing the Italian city-state republics of the Medieval period, as well as the United States and other modern democratic republics. The Julian calendar of ancient Rome formed the basis of the standard modern Gregorian calendar, while Roman inventions and engineering, such as the construction of concrete domes, continued to influence various peoples after the fall of Rome. Roman models of colonialism and warfare became influential.

Latin became the lingua franca of the early Roman Empire and later of the Western Roman Empire, while – particularly in the Eastern Roman Empire – indigenous languages such as Greek and to a lesser degree Egyptian and Aramaic continued in use. Despite the decline of the Western Roman Empire, the Latin language continued to flourish in the very different social and economic environment of the Middle Ages, not least because it became the official language of the Roman Catholic Church. Koine Greek, which served as a lingua franca in the Eastern Empire, remains in use today as a sacred language in some Eastern Orthodox churches.

In Western and Central Europe and in parts of northern Africa, Latin retained its elevated status as the main vehicle of communication for the learned classes throughout the Middle Ages and subsequently; witness especially the Renaissance and Baroque periods. Books which had a revolutionary impact on science, such as Nicolaus Copernicus' De revolutionibus orbium coelestium (1543), were composed in Latin. This language was not supplanted for scientific purposes until the 18th century, and for formal descriptions in zoology as well as botany it survived to the later 20th century. The modern international binomial nomenclature holds to this day: taxonomists assign a Latin or Latinized scientific name to each species.

In the 21st century, the Romance languages, which comprise all languages that descended from Latin, are spoken by more than 920 million people as their mother tongue, and by 300 million people as a second language, mainly in the Americas, Europe, and Africa. Romance languages are either official, co-official, or significantly used in 72 countries around the world.^{[failed verification]} Of the United Nations' six official languages, two (French and Spanish) descend from Latin.

Additionally, Latin has had a great influence on the lexicon of West Germanic languages. Romance words make respectively 59%, 20%, and 14% of English, German, and Dutch vocabularies. Those figures can rise dramatically when only non-compound and non-derived words are included. Accordingly, Romance words make roughly 35% of the vocabulary of Dutch. Of all the loanwords in Dutch, 32.2% come directly from some form of Latin (excluding loans from Romance languages). Up to 60% of Albanian vocabulary consists of Latin roots, causing Albanian to once have been mistakenly identified as a Romance language.

All three official scripts of the modern European Union—Latin, Greek, and Cyrillic—descend from writing systems used in the Roman Empire. Today, the Latin script, the Latin alphabet spread by the Roman Empire to most of Europe, and derived from the Phoenician alphabet through an ancient form of the Greek alphabet adopted and modified by Etruscan, is the most widespread and commonly used script in the world. Spread by various colonies, trade routes, and political powers, the script has continued to grow in influence. The Greek alphabet, which had spread throughout the eastern Mediterranean region during the Hellenistic period, remained the primary script of the Eastern Roman Empire through the Byzantine Empire until its demise in the 15th century. Cyrillic scripts largely derive from the Greek.