Portugal is a fairly linguistically and religiously homogeneous country. Ethnically the Portuguese people form 95% of the total population in Portugal. The Portuguese people are mainly a combination of ancient paleolithic populations, and the proto-Celtic, Celtic and Iberian tribes, para-Celtic Lusitanians.

From Proto-Celtic to Old Irish, the most important changes are these: Lenition and palatalisation, multiplying the entire set of consonants by 4. See #History for more details. Loss of most final consonants. See #Syncope in detail. Proto-Celtic *s is lenited to /h/, which then disappears between vowels.