Peru has three main drainage systems. One comprises about 50 torrential streams that rise in the sierra and descend steeply to the coastal plain. The second comprises the tributaries of the Amazon River in the montaña region. In the third the principal feature is Lake Titicaca, which drains into Lake Poopó in Bolivia through the Desaguadero River.
The Napo, Tigre, and Pastaza rivers rise in Ecuador and flow into Peru. The latter two streams are tributaries of the Marañón River, and the Napo empties into the Amazon River. The border between Peru and Colombia is delineated by the Putumayo River.

The climate of Peru varies widely, ranging from tropical in the montaña to arctic in the highest mountains of the Andes. Average temperatures decrease about 1.7 Celsius degrees (about 3 Fahrenheit degrees) with every 450-m (1,500-ft) increase in elevation. Permanent snow and ice fields cover peaks more than 5,000 m (16,500 ft) above sea level, and the highest elevation at which the land is suitable for agriculture is about 4,400 m (14,500 ft).
In the coastal plain the temperature is normally equable, averaging about 20°C (about 68°F) throughout the year. The coastal climate is moderated by winds blowing from the cool offshore current known as the Peru, or Humboldt, Current. The coast receives less than 50 mm (2 in) of precipitation each year, largely because the cordilleras receive most of the rain carried by the trade winds from the east. Mist-laden clouds known as garúa shroud many of the slopes of the sierra from June to October, providing enough moisture to support grasslands.
In the sierra the temperature ranges seasonally from about -7° to 21°C (about 20° to 70°F). Rainfall is usually scanty, but in some localities heavy rains fall from October to April. In Cuzco, in the southeastern sierra, annual rainfall averages some 815 mm (32 in). The exposed eastern slopes of the Andes receive more than 2,500 mm (100 in) of rain annually, but sheltered locations receive much less. Rainfall amounts diminish rapidly southward, causing many changes in the vegetation.
The montaña region is extremely hot and humid, although at higher elevations it is less so. The prevailing easterly winds blowing across that region gather moisture that is later deposited on the eastern Andean slopes. Annual rainfall in some districts averages as much as 3,810 mm (150 in). Most of this rain, which principally falls from November through April, eventually drains back to the montaña.
Peru's climate periodically experiences a weather pattern known as El Niño. El Niño occurs every three to seven years when unusually warm ocean conditions appear along the western coast. During El Niño the wet weather conditions normally present in the western Pacific move to the east, bringing heavy rains that can cause extensive flooding.

Mineral deposits, the primary resources of Peru, include petroleum, found on the northwestern coast and in the Amazon Basin; copper in northwestern Peru; and substantial deposits of silver, iron ore, gold, lead, and zinc throughout the cordilleras. Also important are the forests, especially the stands of cedar, oak, and mahogany.

The plant life of the three main geographical regions varies widely. The vast, fertile montaña contains a rich profusion of trees, plants, and jungle vines, including mahogany, cedar, rubber, and cinchona trees, sarsaparilla and vanilla plants, and a variety of exotic tropical flowers. The rugged sierra supports a relatively sparse plant life. Sierra vegetation is largely xerophytic—that is, adapted to survival on a restricted supply of water. Such growths include mesquite, cactus, scrub and fodder grasses, and eucalyptus plants. The dry, sandy reaches of the coastal plain support mainly desert vegetation, such as shrubs, grasses, and tuberous plants.
he wildlife of coastal Peru is limited in number and variety. The coastal plain and offshore islands support gulls and terns and some albatrosses, but little other wildlife except lizards, insects, tarantulas, and scorpions. Peruvian ocean waters abound in anchovy, pilchard, haddock, sole, mackerel, smelt, flounder, lobster, shrimp, and other marine species. In the sierra are found the llama, alpaca, vicuña, chinchilla, and huanaco. Birds of the region include the giant condor, robin, phoebe, flycatcher, finch, partridge, duck, and goose. Lake Titicaca and other sierran bodies of water teem with fish. Animals of the tropical montaña include the jaguar, cougar, armadillo, peccary, tapir, anteater, several dozen species of monkey, alligator, turtle, and a variety of snakes and insects; among the birds are the parrot, the flamingo, and other tropical species.

About 45 percent of Peru's inhabitants are Native Americans, some of whom are descended from the Inca who established a great civilization in the region by the 15th century. About 100 other indigenous groups live in the rain forest of eastern Peru. These tribes live in virtual isolation from the rest of Peru's population, speaking traditional languages and surviving by hunting, fishing, and agriculture. Some 37 percent of the country's people are mestizos, those of mixed white (mainly Spanish) and Native American background. About 15 percent of Peruvians are of unmixed white descent, and many of the remainder are of black African, Japanese, or Chinese ancestry. Some 73 percent of the people live in urban areas.Politically and economically, Peru is a divided society. At the top of the social structure is a minority of Spanish-speaking Europeans living on the coast, and especially in
Lima. They control most of the country's wealth and political power. At the bottom are Quechua- and Aymara-speaking Native Americans living in the highlands and in the shantytowns surrounding Arequipa, Lima, and other coastal cities. In between is a largely mestizo middle class of professionals, businessmen, army officers, and government employees.
The military government that ruled from 1968 to 1980 carried out several reforms to curtail the power of wealthy Peruvians and benefited people in the middle and lower-middle classes. These reforms redistributed land to highland Native Americans, turned sugar plantations over to worker cooperatives, and extended the government's role in all sectors of the economy. In the end, however, soaring inflation and unemployment left the mass of Peruvians as poor as they were before the reforms, and the majority still have a very low standard of living. Much of rural Peru lacks electricity, safe drinking water, adequate sanitary facilities, and accessible health care, as do most of the shantytowns to which former rural residents emigrated during the later decades of the 20th century.

The population of Peru (2002 estimate) is 27,949,639, giving the country an estimated overall population density of 21 persons per sq km (55 per sq mi). The distribution, however, is uneven, with about 50 percent of the people inhabiting the sierra region and about 40 percent inhabiting the coastal plain.

The largest city in Peru is Lima (greater city population, 1996 estimate, 6,884,000), the country's capital and chief commercial center.Other important cities include Callao (424,294), a major port located near Lima; Arequipa (710,103), an industrial center; Trujillo (603,657), a commercial center; Chiclayo (375,058), in the sugar district; and Cuzco (278,590), famous for its Inca ruins.

Spanish, spoken by some 70 percent of the people, was the sole official language of Peru until 1975, when Quechua, one of the principal languages of the Native Americans, also was made an official language. Another Native American language, Aymará, was declared official in 1980. English is also spoken.
More than 90 percent of Peruvians are Roman Catholic. In 1915 a law was passed that made Roman Catholicism the established religion of the country. However, the constitution of 1979 ended Roman Catholicism's status as the established religion, although it recognized Catholicism “as an important element in the historical, cultural, and moral formation of Peru.” Other religions are permitted and tolerated, and small numbers of Protestants, Jews, and Muslims live in Peru.

The literacy rate in Peru has increased substantially as a result of greater emphasis on education. According to estimates, the adult literate population rose from 42 percent in 1940 to 97 percent in 2001. Public basic education in Peru is free and compulsory for all children between the ages of 6 and 12. Many children in rural areas do not attend secondary school, however, because of a lack of facilities. In 1998 some 4.2 million pupils attended elementary schools, and 2 million students were enrolled in secondary and vocational schools.

Peru's estimated gross domestic product (GDP) in 1999 was $51.9 billion. Although the economy remains primarily agricultural, the mining and fishing industries have become increasingly important. Peru relies primarily on the export of raw materials—chiefly minerals, farm products, and fish meal—to earn foreign exchange for importing machinery and manufactured goods. During the late 1980s, guerrilla violence, rampant inflation, chronic budget deficits, and drought combined to drive the country to the brink of fiscal insolvency. However, in 1990 the government imposed an austerity program that removed price controls and ended subsidies on many basic items and allowed the inti, the national currency at that time, to float against the United States dollar.

Some 5 percent of Peru's working population is engaged in farming, forestry, or fishing.Most of the coastal area is devoted to the raising of export crops; on the montaña and the sierra are mainly grown crops for local consumption. Many farms in Peru are very small and are used to produce subsistence crops; the country also has large cooperative farms.

The chief agricultural products, together with the yield (in metric tons) in 2001, were sugarcane (7.9 million), root crops such as potatoes (4.3 million), rice (2 million), corn (1,418,000), seed cotton (134,300), coffee (158,200), and wheat (190,200). Peru is the world's leading grower of coca, from which the drug cocaine is refined. The livestock population included 4.9 million cattle, 14.5 million sheep, 2 million goats, 2.8 million hogs, 690,000 horses, 250,000 mules, and 90 million poultry. Llamas, sheep, and vicuñas provide wool, hides, and skins

The unit of currency in Peru is the nuevo sol, divided into 100 céntimos (3.38 nuevo sols equal U.S.$1; 1999 average). The nuevo sol replaced the previous currency, the inti, in 1991 (1 nuevo sol equaled 1 million inti). The inti had replaced the sol in 1985 at a rate of 1,000 to 1. The Banco Central de Reserva del Perú (1922) is the central bank and bank of issue. All private domestic banks were nationalized in 1987. The largest of these, Interbanc, was reprivatized in 1994.Exports are more diversified in Peru than in most South American countries. The principal exports are petroleum, copper, lead, coffee, silver, fish meal, zinc, sugar, and iron ore. The chief export markets are the United States, Japan, the United Kingdom, China, and Germany. Exports earned $7 billion in 2000. The leading imports of Peru include electrical and electronic items, foodstuffs, metals, chemicals, and transportation equipment. The principal sources of these goods are the United States, Colombia, Chile, Venezuela, and the United Kingdom. Imports cost $8.8 billion in 2000. Peru is a member of two international trade organizations, the Latin American Integration Association (LAIA), which replaced the former Latin American Free Trade Association in 1980; and the Andean Group. The LAIA works to integrate the economies of all of Latin South America while the Andean Group does the same for its members, which also include Bolivia, Colombia, Ecuador, and Venezuela.

The Inca, sometimes called peoples of the sun, were originally a warlike tribe living in a semiarid region of the southern sierra. From 1100 to 1300 the Inca moved north into the fertile Cuzco Valley. From there they overran the neighboring lands. By 1500 the Inca Empire stretched from the Pacific Ocean east to the sources of the Paraguay and Amazon rivers and from the region of modern Quito in Ecuador south to the Maule River in Chile. This vast empire was a theocracy, organized along socialistic lines and ruled by an Inca, or emperor, who was worshiped as a divinity. Because the Inca realm contained extensive deposits of gold and silver, it became in the early 16th century a target of Spanish imperial ambitions in the Americas.

In November 1995 anthropologists announced the discovery of the 500-year-old remains of two Inca women and one Inca man frozen in the snow on a mountain peak in Peru. Scientists concluded that the trio were part of a human sacrifice ritual on Ampato, a sacred peak in the Andes mountain range. Artifacts from the find unveiled new information about the Inca and indicated the use of poles and tents rather than traditional stone structures. The arrangement of doll-size statuettes dressed in feathers and fine woolens provided clues about Inca religious and sacrificial practices.