Tagalog (/təˈɡɑːlɒɡ/;Tagalog pronunciation: [tɐˈɡaːloɡ]) is an Austronesian language spoken as a first language by a third of the population of the Philippines and as a second language by most of the rest. It is the first language of the Philippine region IV (CALABARZON and MIMAROPA) and of Metro Manila. Its standardized form, commonly called Filipino, is the national language and one of two official languages of the Philippines. It is related to other Austronesian languages such as Malay, Javanese, and Hawaiian.

The word Tagalog derived from tagailog, from tagá- meaning "native of" and ílog meaning "river". Thus, it means "river dweller". Very little is known about the history of the language. However, according to linguists such as Dr. David Zorc and Dr. Robert Blust, the Tagalogs originated, along with their Central Philippine cousins, from Northeastern Mindanao or Eastern Visayas.

The first written record of Tagalog is in the Laguna Copperplate Inscription, written in the year 900, using fragments of the language along with Sanskrit, Malay, and Javanese. Meanwhile, the first known book to be written in Tagalog is the Doctrina Cristiana (Christian Doctrine) of 1593. It was written in Spanish and two transcriptions of Tagalog; one in the Baybayin script and the other in Latin script. Throughout the 333 years of Spanish occupation, there were grammar and dictionaries written by Spanish clergymen such as Vocabulario de la Lengua Tagala by Pedro de San Buenaventura (Pila, Laguna, 1613), Vocabulario de la lengua tagala (1835) and Arte de la lengua tagala y manual tagalog para la administración de los Santos Sacramentos (1850). Poet Francisco Baltazar (1788–1862) is regarded as the foremost Tagalog writer. His most notable work is the early 19th-century Florante at Laura.