The isolation created by the mountainous terrain is so great that some groups, until recently, were unaware of the existence of neighboring groups only a few kilometers away. The diversity, reflected in a folk saying, "For each village, a different culture," is perhaps best shown in the local languages. Spoken mainly on the island of New Guinea--composed of Papua New Guinea and the Indonesian province of West Papua--some 800 of these languages have been identified; of these, only 350-450 are related. The remainder seem to be totally unrelated either to each other or to the other major groupings. Most native languages are spoken by a few hundred to a few thousand, although Enga, used in part of the highlands, is spoken by some 130,000 people. (However, the Enga are subdivided into clans that regularly conflict with each other.) Many native languages are extremely complex grammatically.

Melanesian Pidgin serves as the lingua franca. English is spoken by educated people and in Milne Bay Province.

The overall population density is low, although pockets of overpopulation exist. Papua New Guinea's Western Province averages one person per square kilometer (3 per sq. mi.). The Chimbu Province in the New Guinea highlands averages 20 persons per square kilometer (60 per sq. mi.) and has areas containing up to 200 people farming a square kilometer of land. The highlands are home to 40% of the population.

A considerable urban drift toward Port Moresby and other major centers has occurred in recent years. The trend toward urbanization accelerated in the 1990s, bringing in its wake squatter settlements, ethnic disputes, unemployment, and attendant social problems, especially violent crime.

Almost two-thirds of the population is Christian. Of these, more than 700,000 are Catholic, more than 500,000 Lutheran, and the balance are members of other Protestant denominations. Although the major churches are under indigenous leadership, a large number of missionaries remain in the country. The bulk of the estimated 2,500 Americans resident in Papua New Guinea are missionaries and their families. The non-Christian portion of the indigenous population, as well as a portion of the nominal Christians, practice a wide variety of religions that are an integral part of traditional culture, mainly animism (spirit worship) and ancestor cults.

Foreign residents comprise about 1% of the population. More than half are Australian; others are from the United Kingdom, New Zealand, the Philippines, and the United States, most of whom are missionaries. Since independence, about 900 foreigners have become naturalized citizens.

Though cultures vary widely, traditional Papua New Guinea social structures generally include the following characteristics:

The practice of subsistence economy;
Recognition of bonds of kinship with obligations extending beyond the immediate family group;
Generally egalitarian relationships with an emphasis on acquired, rather than inherited, status; and
A strong attachment of the people to land, which is held communally. Traditional communities do not recognize a permanent transfer of ownership when land is sold.
Though land and other possessions may be inherited through the female line in some cultures, women generally are considered and treated as inferiors. Gender violence is endemic.
Patterns and frequency of sexual activity, though never publicly discussed, contribute to the current rapid spread of HIV.

Most Papua New Guineans still adhere strongly to this traditional social structure, which has its roots in village life.