Portugal is a fairly homogeneous country linguistically and religiously. Ethnically, Portuguese are a combination of several ethnicities: pre-Roman Celtic and Iberian tribes with Romans, and Germanic tribes. Moors became a reduced influence, as a significant number was expelled during the Reconquista. There is also ethnical influence from other Mediterranean civilizations. Today, Portuguese people are reasonably homogenous. Portugal's biggest metropolitan agglomerations are Lisbon, Porto, Braga, Aveiro, and Coimbra.

The first census in Portugal dates from 1864. But, in the 16th century, John III called for a populational count in continental Portugal and between 1527 and 1532 there was a population of 1 to 1.4 million. In 1801, there were circa 2,913,000 inhabitants.

Between 1960 and 1970, more than one million Portuguese emigrated, mostly to other European countries, resulting in a negative evolution of the population. Previously, Brazil has been the destination of many, especially since the 18th century. Since mid 1970s major changes started to influence the country's demography as life expectancy went up; the infant mortality rate and the fertility rate broadly declined; and, with the decolonisation, many Portuguese (including mixed-raced) returned from Africa.

In the 2001 Census, Portugal had 10,356,117 inhabitants (51,7% female). Currently, there are almost 10,6 million inhabitants and most of the population growth is immigration derived. In the end of 2003, legal immigrants represented 4.2% of the population, and the largest communities were: Ukrainians (15%), Brazilians (14.8%), Cape Verdeans (14.4%), and Angolans (7.9%). Counting illegal immigrants, estimates indicate there is almost 1 immigrant per 10 citizens in Portugal.

The great majority of the Portuguese population belongs to the Roman Catholic Church. Religious observance remains strong in northern areas, with the population of Lisbon and southern areas generally less devout. Religious minorities include a little over 300,000 Protestants. There are also about 50,000 Muslims and 10,000 Hindus. Most of them came from Goa, a former Portuguese colony on the west coast of India. There are also about 1,000 Jews, but a large number of people have some Jewish heritage.

The country is characterized by city, town or village cultural differentiation and there is virtually no regional affiliation, unlike other European countries. Portuguese is spoken throughout the country, with only the villages of Miranda de Douro's Mirandese language recognised as a local language.