In mid-1985, Spain's population reached 38.8 million, making it Western Europe's 5th most populous nation. The nation's population grew very slowly throughout the latter half of the nineteenth century and most of the twentieth. In the 1860s, the population increased by only about one-third of 1% annually; by the first decades of the twentieth century, this rate of increase had grown to about 0.7% per year. Between the 1930s and the 1980s, population growth rates hovered between 0.8 and 1.2% annually. In the postwar years, Spain began to exhibit population growth patterns very similar to those of most other advanced industrial societies. Growth rates were projected to level off, or to decline slightly, through the remainder of the twentieth century; Spain was expected to reach a population of 40 million by 1990 and 42 million by the year 2000. Observers around that the nation's population would stabilize in the year 2020 at about 46 million.

Spain has been invaded and colonised by many different peoples. The peninsula was originally settled by groups from North Africa and western Europe, including the Iberians, Celts, and Basques. Throughout antiquity it was a constant point of attraction for the more advanced civilizations of the eastern Mediterranean. From about 1100 BC the Phoenicians, the Greeks, and the Carthaginians began to establish settlements and trading posts, particularly on the eastern and southern coasts.