Historically, the Galician-Portuguese language originated in Galicia and Northern Portugal in lands belonging to the ancient Kingdom of Galicia (comprising the Roman Gallaecia,) and branched out since the 14th century after the Portuguese expansion brought it southwards. There are linguists who consider Modern Galician and Modern Portuguese as dialects or varieties of the same language, but this is a matter of debate. For instance, in past editions of the Encyclopædia Britannica, Galician was termed a Portuguese dialect spoken in northwestern Spain, once often incorrectly considered a dialect of Spanish. However, the Galician government does not regard Galician as a variety of Portuguese, but rather as a separate language. Mutual intelligibility (estimated at 85% by R. A. Hall, Jr., 1989) is good between Galicians and Northern Portuguese, but poorer between Galicians and speakers of Central-Southern European Portuguese. The dialects of Portuguese most similar to Galician are those of Alto-Minho and Trás-os-Montes (Northern Portugal).
The relationship involving Galician and Portuguese can be compared with that between Flemish and Dutch, Macedonian and Bulgarian, or Occitan and Catalan. Due to language proximity two interpretations have risen in conflict:
The official institution regulating Galician language is Instituto da Lingua Galega (ILG). It claims that modern Galician must be considered an independent Romance language that belongs to the group of Ibero-Romance Languages and has strong ties with Portuguese and its northern dialects.There is also an unofficial and minoritary institution Associaçom Galega da Língua (AGAL), according to which differences between Galician and Portuguese languages are not enough to consider them separate languages, just like other Galician-Portuguese forms such as Brazilian Portuguese, African Portuguese, archaic Galician-Portuguese still spoken in Spanish Extremadura Fala, and other dialects.