Portuguese (endonym: português or língua portuguesa) is a Western Romance language of the Indo-European language family originating from the Iberian Peninsula of Europe. It is spoken chiefly in Brazil, Portugal, and several countries in Africa, as well as by immigrants in North America, Europe, and South America. With approximately 267 million speakers, it is listed as the fifth-most spoken native language.

Portuguese-speaking people or nations are known as Lusophone (lusófono). As the result of expansion during colonial times, a cultural presence of Portuguese speakers is also found around the world. Portuguese is part of the Ibero-Romance group that evolved from several dialects of Vulgar Latin in the medieval Kingdom of Galicia and the County of Portugal, and has kept some Celtic phonology.

Portuguese language structure reflects its Latin roots and centuries of outside influences. These are seen in phonology, orthography, grammar, and vocabulary. Phonologically, Portuguese has a rich system of nasal vowels, complex consonant variations, and different types of guttural R and other sounds in European and Brazilian varieties. Its spelling, based like English on the Latin alphabet, is largely phonemic but is influenced by etymology and tradition. Recent spelling reforms attempted to create a unified spelling for the Portuguese language across all countries that use it. Portuguese grammar retains many Latin verb forms and has some unique features such as the future subjunctive and the personal infinitive. The vocabulary is derived mostly from Latin but also includes numerous loanwords ^[pt] from Celtic, Germanic, Arabic, African, Amerindian, and Asian languages, resulting from historical contact including wars, trade, and colonization.

There is significant variation in dialects of Portuguese worldwide, with two primary standardized varieties: European Portuguese and Brazilian Portuguese, each one having numerous regional accents and subdialects. African and Asian varieties generally follow the European written standard, though they often have different phonological, lexical, and sometimes syntactic features. While there is broad mutual intelligibility among varieties, variation is seen mostly in speech patterns and vocabulary, with some regional differences in grammar.

When the Romans arrived in the Iberian Peninsula in 216 BC, they brought with them the Latin language, from which all Romance languages are descended. The language was spread by Roman commoners, merchants, and soldiers, who built Roman cities mostly near the settlements of previous Celtic civilizations established long before the Roman arrivals. For that reason, the language has kept a relevant substratum of much older, Atlantic European Megalithic Culture and Celtic culture, part of the Hispano-Celtic group of ancient languages. In Latin, the Portuguese language is known as lusitana or (latina) lusitanica, after the Lusitanians, a pre-Celtic tribe that lived in the territory of present-day Portugal and Spain that adopted the Latin language as Roman settlers moved in. This is also the origin of the luso- prefix, seen in terms like "Lusophone".

Between AD 409 and AD 711, as the Roman Empire collapsed in Western Europe, the Iberian Peninsula was conquered by Germanic peoples of the Migration Period. The occupiers, most notably Suebi but also Visigoths and Buri originally spoke Germanic languages. Quickly, they adopted late Roman culture and the Vulgar Latin dialects of the peninsula and over the next 300 years totally integrated into the local population. Some Germanic words from that period are part of the Portuguese lexicon, together with place names, surnames, and first names.

With the Umayyad conquest beginning in 711, Arabic became the administrative and common language in the conquered regions, but most of the remaining Christian population continued to speak a form of Ibero-Romance called Mozarabic which introduced a few hundred words from Arabic, Persian, Turkish, and Berber. Like other Neo-Latin and European languages, Portuguese has adopted a significant number of loanwords from Greek, mainly in technical and scientific terminology. These borrowings occurred via Latin, and later during the Middle Ages and the Renaissance.

Portuguese evolved from the medieval language spoken in the northwestern medieval Kingdom of Galicia, which the County of Portugal once formed part of. This variety has been retrospectively named Galician–Portuguese, Old Portuguese, or Old Galician by linguists.