The peninsula consists of a limestone and shale ridge known as the Rock, which rises abruptly from the isthmus to 1,380 feet (421 metres) at Rock Gun, its northernmost summit. Its highest point, 1,396 feet (426 metres), is attained near its southern end. The Rock shelves down to the sea at Europa Point, which faces Ceuta (a Spanish enclave in Morocco), about 20 miles (30 km) to the south across the strait. From the Mediterranean, Gibraltar appears as a series of sheer, inaccessible cliffs, fronting the sea on the peninsula's east coast. The Rock's slope is more gradual on its western side and is occupied by tier upon tier of houses that stretch for some 300 feet (90 metres) above the old defensive walls. Higher up, limestone cliffs almost isolate the Upper Rock, which is covered with a tangle of wild trees.

Gibraltar has no springs or rivers, and an area of sand slopes above Catalan and Sandy bays has been sheeted over to provide a rain-catchment area, which was once the sole source of potable water for Gibraltar. The water was stored in a number of tanks blasted into the Rock. The rainwater was then blended with water pumped from wells on the isthmus or distilled from the sea. The catchment ceased to be used as a source of potable water in the 1990s, when a desalinization plant built in the 1980s was expanded, but it still is used as a service reservoir. Gibraltar has hot, humid, and almost rainless summers; mild winters during which there is usually adequate rain; and warm, moderately rainy transitional seasons.

There are more than 500 species of small flowering plants on Gibraltar, and the Gibraltar candytuft is a flower native only to the Rock. Wild olive and pine trees grow on the Upper Rock. Mammals include rabbit, fox, and Barbary macaque (often erroneously identified as apes). Barbary macaques have roamed the Rock for hundreds of years and are Europe's only wild monkeys. Although free to wander, they are generally seen on the Upper Rock. The macaques were once protected by the British army in Gibraltar, and, according to legend, British dominion over the Rock will cease when these animals are no longer present; their protection is now the responsibility of the Gibraltar Ornithological and Natural History Society. Migratory birds are common, and Gibraltar is the home of the only specimens of Barbary partridge in Europe.

Gibraltar is considered one of the two Pillars of Heracles (Hercules), the other being Mount Hacho, on the African coast opposite. The Pillars, which according to Homer were created when Heracles broke the mountain that had connected Africa and Europe, defined the western limits of navigation for the ancient Mediterranean world. Since the 18th century Gibraltar has been a symbol of British naval strength, and it is commonly known in that context as “the Rock.” With the opening of the Suez Canal in 1869, Gibraltar increased in strategic importance, and its position as a provisioning port was greatly enhanced. Since World War II the British military garrison and naval dockyard have continued to be an important part of Gibraltar's economy, and naval operations of the North Atlantic Treaty Organization (NATO) often use the port facilities.

Gibraltar is an overseas territory of the United Kingdom (British Empire) and is self-governing in all matters but defense. In 1981 Gibraltarians were granted full British citizenship; Gibraltarians age 18 or older and British civilians resident for more than six months are entitled to vote. The governor, appointed by the British sovereign, is the head of the executive and is advised by the Gibraltar Council. The governor appoints the Council of Ministers, composed of the chief minister and other ministers, from the party or coalition of parties that gains a majority of seats in the House of Assembly. The House of Assembly consists of the speaker (appointed by the governor), 15 members elected to four-year terms, and 2 ex-officio members. Instead of a city council, one minister is responsible for municipal affairs.

Because of lack of space on the peninsula, there is no agriculture. There is a small amount of light industry—tobacco, beverages, canning—but the main sources of income are the provisioning of ships and military personnel, tourism, and the re-export trade. Tourism has been stimulated through the large-scale expansion of hotel and beach facilities and gambling casinos. The port facilities occupy most of the western shore and a portion of land reclaimed from the sea. Income and customs taxes produce most of the colony's revenue. The United Kingdom supplies a significant amount of development aid. Principal expenditures include social services, public works, and municipal services. Gibraltar joined the European Community (now embedded in the European Union) with the United Kingdom in 1973. The monetary unit is the Gibraltar pound.

Passenger and cargo vessels stop at Gibraltar's port, and ferries cross daily to Tangier, Morocco. Regular flights link Gibraltar to London and Manchester. The peninsula has a road system and a system of tunnels within the Rock for vehicular traffic. A cable car ascends to the central summit of the ridge.

About four-fifths of the population are Gibraltarians, which includes those born in Gibraltar before 1925 and their descendants, as well as the spouses of Gibraltarians. The remainder are resident aliens and the families of British military personnel. Most Gibraltarians are of mixed Genoese, British, Spanish, Maltese, and Portuguese descent. Moroccans and Indians predominate among the resident aliens.

About four-fifths of Gibraltarians are Roman Catholic. The Anglican bishopric also covers communities in southern Europe. The small Jewish community is of Sephardic descent. English is the official language of government and education, though most Gibraltarians are bilingual in English and Spanish, and many speak an English dialect known as Yanito (Llanito), which is influenced by Spanish, Genoese, and Hebrew.

Education is free and compulsory between ages 5 and 15. Educational facilities include several government primary schools and two comprehensive secondary schools. There are also private and military institutions, a school for children with disabilities, and a technical college.

Excavations of limestone caves in the Rock have revealed that Gibraltar was sporadically inhabited from prehistoric times. The Muslim commander Ṭāriq ibn Ziyād captured Gibraltar in 711, and the site was thereafter held as a fortress by all its successive occupiers. The Muslim occupation was permanently ended by the Spanish in 1462, and Isabella I annexed Gibraltar to Spain in 1501. But in 1704, during the War of the Spanish Succession (Spanish Succession, War of the), Sir George Rooke captured Gibraltar for the British, and Spain formally ceded it to Britain under the terms of the Treaty of Utrecht (Utrecht, treaties of) in 1713. The Spanish nevertheless made several attempts to retake Gibraltar from Britain, most notably in a protracted but unsuccessful military siege that lasted from 1779 to 1783. In 1830 Gibraltar became a British crown colony. The opening of the Suez Canal (1869) heightened British determination to keep possession of Gibraltar, since the Mediterranean was now the main route to Britain's colonies in East Africa and southern Asia.

Early in the 20th century the Rock was tunneled to facilitate communication between the peninsula's east and west sides, and the excavated material was used to reclaim 64 acres (26 hectares) from the sea and thus expand the area of the cramped settlement. Gibraltar was a vital repair and assembly point for Allied convoys during the world wars. In the 1960s the Spanish government stepped up its demands for the “decolonization” of Gibraltar. A referendum in Gibraltar in 1967 gave the colony's residents a choice of opting either for Spanish sovereignty or for continued close association with Britain; the result was an overwhelmingly pro-British vote (12,138 votes to 44). The new constitution that Britain introduced for Gibraltar in 1969 explicitly reaffirmed Gibraltar's link with Britain while also granting it full internal self-government. Spain responded by closing its border with Gibraltar, thus depriving the colony of its Spanish trade and a labour force of Spanish commuters. Spain lifted its border blockade in 1985.

The status of Gibraltar has remained a source of friction between the Spanish and British governments. In a nonbinding referendum in 2002 recognized by neither government, 99 percent of Gibraltar's voters rejected joint British-Spanish sovereignty. Gibraltar subsequently was allowed by both governments to represent itself in negotiations on its future. Area including port and harbour water, 2.5 square miles (6.5 square km). Pop. (2003 est.) 28,605.