Pennsylvania is classified as a Middle Atlantic state, along with New York, New Jersey, Delaware, and Maryland. Its central location on the Eastern Seaboard is sometimes said to be the source of its nickname, the Keystone State. It does not, however, touch the Atlantic Ocean at any point.Water nonetheless has been nearly as crucial in the state's growth as the wealth of its earth. The Delaware River forms the boundary between Pennsylvania and New Jersey. In the northwest a small panhandle separates Ohio and New York and forms a 40-mile (65-km) waterfront on Lake Erie, giving the state access to the iron-ore barges and other commerce of the Great Lakes.

The state has two great metropolitan areas. Philadelphia is a part of the East Coast population belt stretching from Boston to Norfolk, Va. It is a major harbour on the Delaware River and one of the world's busiest shipping centres. In the west, Pittsburgh lies on the eastern edge of the great industrial region extending along the Great Lakes plains to Chicago. Area 46,056 square miles (119,284 square km). Pop. (2000) 12,281,054; (2007 est.) 12,432,792.

Beginning about 250 million years ago, plate-tectonic movement folded the flat-lying sediment into upwarps and downwarps. The heat created by this pressure also metamorphosed the rocks, changing the sandstone into quartzite, limestone into marble, and granite into gneiss. The pressure from the plate movement was confined to southeastern Pennsylvania, creating the Piedmont and Ridge and Valley provinces. The rocks of the Appalachian Plateau remained essentially flat-lying, and the dissection of the plateau has been created by erosion.

Pennsylvania includes parts of large physiographic regions that extend beyond its borders; those regions crossing the eastern and central parts of the state parallel one another along a sweeping northeast-southwest diagonal orientation. In the southeastern part of the state is a section of the Atlantic Coastal Plain, a narrow strip of sandy low-lying land immediately adjacent to the Delaware River. This region has played a major role in Pennsylvania history. It was the site of William Penn's settlement and the initial city of Philadelphia. Immediately inland from the Coastal Plain is the Piedmont province, a gently rolling, well-drained plain that is rarely more than 500 feet (150 metres) above sea level; the eastern part is the Piedmont Upland. The boundary between the Piedmont and the Coastal Plain is known as the fall line, with hard rock to the west and soft rock to the east. The Piedmont Lowland parallels the Piedmont Upland to its northwest. It is made of sedimentary rocks into which volcanic rocks have been intruded. Some of these volcanic rocks make ridges. The Battle of Gettysburg (Gettysburg, Battle of) was fought there, the Northern army on the high ridges having the advantage over the Southern forces on the plains. The limestone rocks have weathered into fertile lowlands such as the Conestoga Lowlands of Lancaster county. Farther to the northwest lie two segments of a larger mountain range. The southern prong, extending to the Carlisle area, is the northernmost extension of the Blue Ridge system. The northern portion, known as the Reading Prong, is a small section of the larger New England topographic region. There is a major gap between these prongs.

Inland from the Blue Ridge is one of the country's most distinctive topographic regions, the Ridge and Valley Province. It consists of long, narrow valleys and parallel ridges aligned over a long distance. As seen from space, it appears as if an enormous rake had been dragged along the backbone of the Appalachians from northeast to southwest. None of the ridges rises above the valley floor more than 1,000 feet (300 metres), and nowhere does the elevation reach 3,000 feet (900 metres). On the east is the Great Valley, which stretches more than 1,200 miles (1,930 km) from Pennsylvania to Alabama. To the west and north of the Ridge and Valley Province is the Appalachian Plateau, an area of nearly 30,000 square miles (77,700 square km). The Allegheny Front, more than 1,500 feet (450 metres) high, divides the two provinces. With no passes, it is the most formidable obstacle to east-west transportation in Pennsylvania. Almost everywhere the plateau surface has been dissected by rivers into a chaos of valleys and hills. Mount Davis (Davis, Mount) is the highest point in the state at 3,213 feet (979 metres). However, elevations range from about 1,000 to 3,000 feet. On the northwest is the narrow Lake Erie Plain, which rises in a series of steps from the lakeshore to the high escarpment of the Appalachian Plateau.

Pennsylvania generally has a humid continental climate characterized by wide fluctuations in seasonal temperatures, with prevailing winds from the west. The average temperature in July is about 70 °F (21 °C) and in January about 28 °F (− 2 °C). The growing season varies from nearly 200 days in the southeast to only 90 days in the north-central part of the state. On average, about 40 inches (1,000 mm) of precipitation fall in the state annually. The daily weather is influenced by the passage of cyclone fronts in the westerly wind system.

At the time of the first European settlement in 1682, the land surface of Pennsylvania was covered entirely by trees. By about 1900 some three-fourths of the land had been cleared of forests, principally for farmland. Since then, vast areas of farmland have been abandoned, and much of that land has returned to forest cover. About half of the state is now wooded, although only small areas are still virgin forest. Pennsylvania occupies a transition zone between the northern and southern forests of the United States. In the north are beech, maple, birch, pine, and hemlock trees, while in the south oak, hickory, yellow poplar, walnut, and elm dominate.

Pennsylvania's abundant wildlife makes it a leading state for hunting. Not only is there abundant small game—rabbits, pheasants, and squirrels—but tens of thousands of deer and a few hundred black bears are killed by hunters every year. The streams are stocked with fish—trout, walleye, and others—each spring to support sportfishing.

Because of the state's rugged topography, settlement in Pennsylvania proceeded slowly. From Philadelphia, people moved west and north. However, it took about 80 years for settlement to extend west to the Ridge and Valley area of central Pennsylvania. In the western part of the state, the first settlers arrived from Virginia, traveling west by way of the Potomac River and north along the Monongahela River, reaching Pittsburgh in the 1750s. In 1840 settlers reached the last remaining unexploited area—the rugged north-central portion of the state. Thus, it took 160 years from the first settlement for the final pioneer area to be occupied.

There were a few Swedish, Dutch, and Finnish settlers in Pennsylvania prior to William Penn's arrival. Initially, English Quakers (Friends, Society of) (adherents of the Society of Friends (Friends, Society of)) were the most important group to occupy the Delaware valley. Philadelphia, along with nearby Chester and Bucks counties, became the first thriving agricultural commercial region.

The next major group to settle in Pennsylvania comprised Scotch-Irish from Northern Ireland. To find farmland they moved westward beyond the English and the Germans to the western Piedmont and the Ridge and Valley region. By the time of the Revolution, they constituted one-fourth of the total population of the colony. The fourth major group, the Irish, emigrated from their homeland in the 1840s and '50s because of the Irish Potato Famine.

The Industrial Revolution spurred the development of a dynamic economy in Pennsylvania. Because the domestic population was inadequate to supply the needed labour, the state became the centre of a massive migration of Italians, Poles, Russians, Ukrainians, and people from the Balkan region, among others. Between 1890 and 1900 the population of the state rose to more than a million, largely because of immigration to the mining areas and new industrial centres. In the 20th century, African Americans began to move into the state from the South; they now constitute about one-tenth of the state's total population. Asians, Hispanics, and Native Americans collectively constitute only a small fraction of the population.

The population of Pennsylvania has been nearly stable since reaching 10.5 million in 1950, having increased by only a few million in subsequent decades. Through the late 20th and early 21st centuries, the state's annual population growth was less than 1 percent.

Pennsylvania has one of the largest rural populations in the United States, and nearly one-third of the state is still under cultivation. Livestock—including dairy and beef cattle, hogs, and sheep—and livestock products are the major components of farm income. Pennsylvania is a major producer of milk, eggs, and poultry; fruits, including peaches, grapes, cherries, and apples; hay; corn (maize); mushrooms; and Christmas trees. Ice cream and sausages are important processed food products.

Hydrocarbons—bituminous (soft) coal, anthracite (hard coal), petroleum, and natural gas—provide a vast majority of the mineral wealth of the state. Pennsylvania has also been a major producer of such nonmetallic minerals as limestone, slate, sand, and gravel. Small iron ore deposits provided the basis of early iron furnaces, but the major deposits of iron ore that were located in Cornwall and Morgantown have since been abandoned.

Bituminous coal beds are located in portions of 33 Pennsylvania counties and constitute more than one-fourth of the state's total area. Maximum production was reached in 1918, when nearly 200 million tons of coal were mined. Since the late 20th century, production has fallen to roughly one-fourth of that annually, owing to competition from petroleum and natural gas as well as the existence now of environmental laws that limit the consumption of sulfur-containing coal. Pennsylvania has the only significant deposits of anthracite in the country. Production peaked in 1917, when more than 100 million tons were mined; however, production has also declined—even more precipitously than it has for bituminous—because of competition from other available energy sources.

Northwestern Pennsylvania was the site of the world's first successful oil well (1859, near Titusville) and its first oil boom, in the 1860s. The state's oil fields are now nearly exhausted, but natural gas production remains significant, and Pennsylvania still has one of the largest oil-refining capacities of any state on the East Coast.

Although coal production is only a fraction of previous levels, coal-fired thermal plants still generate most of the state's electric power, with natural gas and oil also used in considerably lesser amounts. The most serious nuclear accident in the history of American nuclear-power industry occurred at the Three Mile Island plant, near Harrisburg, in 1979. However, nuclear energy still provides about one-third of the state's power generated. Hydroelectric stations and other power sources constitute only a tiny portion of the total.

During Pennsylvania's industrial heyday in the 19th and 20th centuries, the Philadelphia and Pittsburgh regions were its primary centres. Eastern Pennsylvania was noted for lighter manufacturing such as textiles, apparel, metal fabrication, and chemicals. The western part of the state focused on heavy manufacturing such as iron, steel, and machinery.

Employment in industry reached its peak of some 1.5 million in about 1970; however, that number had decreased sharply by the late 1990s. The traditional industries of textiles, apparel, iron and steel, tobacco, and leather products declined rapidly. By the early 21st century the most important industries were those producing fabricated metals, machinery, lumber, and instruments, as well as printing and publishing. Although overall employment in manufacturing had declined, the value of manufactured products continued to make a significant contribution to the state's revenue. In the southeastern counties of Chester, Bucks, Berks, Montgomery, Lancaster, and York, high-technology industries have grown in importance.

Since the mid-20th century the service sector has been a steadily increasing source of employment in Pennsylvania. In 1940 nearly half of the state's labour force was in service jobs, and by the turn of the 21st century that proportion had increased to more than three-fourths of the workforce. The growth in service employment originally came from workers who had been active in mining and agriculture and, later, in manufacturing. Tourism is a significant source of jobs and revenue to the state and is one of the fastest-growing areas of the economy.

The number of people working in finance, insurance, and real estate grew rapidly during the 20th century, particularly in the banking and insurance fields. Real estate, security and commodity brokerages, non-depository credit institutions, and holding and investment offices were other significant employers. In the early 21st century, business services such as advertising, credit reports, and public relations were among the most rapidly growing services in the state.

Since the colonial period, when waterways and trails provided the earliest means of travel, modes of transportation have evolved to serve the changing economy. The first major effort to improve transportation came with the building of a network of improved but unpaved roads in Pennsylvania. The extension of the Old Conestoga Road from Philadelphia to Lancaster was begun in 1721 and completed in 1733. Later that century the Lancaster Turnpike was built, roughly following the Conestoga Road; it was the country's first turnpike. This road-building era was followed by the canal era, which dominated transportation from about 1830 to the 1850s. Canals were superseded by railroads as the primary mode of transportation until the early 20th century.

The modern period of transportation began with the widespread use of motor vehicles. As highways were built and improved, the importance of railroads declined. Today, the only interstate passenger rail service still in operation is Amtrak, which operates routes connecting Philadelphia and Pittsburgh to Washington, D.C., and linking Philadelphia with Harrisburg and cities along the Eastern Seaboard; another line travels along Pennsylvania's Lake Erie shore on a route between Chicago and points east. SEPTA (Southeastern Pennsylvania Transportation Authority) provides regional passenger rail service around the greater Philadelphia area and extending to points in New Jersey in addition to its city bus, subway, and trolley services.

In the 20th century, Pennsylvania's highway system was created in three stages: the establishment of the state road system, the creation of east-west and north-south U.S. highways (aided by federal funds), and the development of the interstate system. The state's highway system, one of the most extensive in the country, includes the Pennsylvania Turnpike, a four-lane limited-access toll road (built 1939–40) joining New Jersey and Ohio; it became a model for modern superhighway construction. The turnpike is paralleled to the north by Interstate 80, known in Pennsylvania as the Keystone Shortway.

Pennsylvania has more than 100,000 miles (160,000 km) of highways; the state has primary responsibility for some two-fifths of the mileage. The remainder of its roads are controlled by counties, townships, boroughs, and cities.

Pennsylvania was an early leader in air transportation. By 1909 air shows were being staged around the state, and in 1918 the country's first airmail service was begun between Washington, D.C., and New York City, with Philadelphia as an intermediate stop. Today, Philadelphia and Pittsburgh are the major air hubs, and Allentown (Lehigh Valley), Erie, Harrisburg, and Wilkes-Barre/Scranton have smaller international airports. Several regional airports provide commuter air service to the larger terminals. There are also some 140 public airports that do not provide regular scheduled service.

The governor is elected for a four-year term and may be reelected for one additional term. Among the main powers of the governor are broad veto power over bills passed in the legislature (General Assembly), including a line-item veto for appropriations bills, and the right to return bills to the Assembly for reconsideration. The General Assembly consists of a Senate of 50 members and a House of Representatives of 203 members. Senators are elected for four-year terms and representatives for two-year terms.

A unified judicial system comprises the Supreme Court, Superior Court, Commonwealth Court, county courts, and a system of lower courts. The seven justices of the Supreme Court are elected for 10-year terms; justices of the peace and of the municipal and traffic courts of Philadelphia are elected for 6-year terms.

Under the constitution, the General Assembly provides rules and regulations for local governments. A major responsibility in this regard is to classify all municipalities—such as cities, boroughs, counties, and townships—by population size. All Assembly regulations must be uniform throughout each class, and no community can secure preferential treatment. Philadelphia is the state's only first-class city and may have special legislation. Pittsburgh and Scranton are classified as second-class cities. The rest of Pennsylvania's cities are designated as third-class. Smaller cities have various governmental forms, while boroughs have elected councils and mayors with limited powers. A 1968 constitutional amendment permitted municipalities to choose home rule.

Between the Civil War and the 1920s, state government was, with a few exceptions in the late 19th century, controlled by the Republican Party. The state government became a seat of “boss rule.” This party domination was broken in the 1930s, and since then the governor and General Assembly have been about evenly divided between Republicans and Democrats. Pennsylvania generally exhibits the characteristic American pattern of rural conservatism and urban liberalism, although locally such labels may bear no relationship to particular parties.

The government provides most of the funds for public social services in Pennsylvania. Since the creation of such programs at the time of Pres. Franklin D. Roosevelt (Roosevelt, Franklin D.)'s New Deal in the 1930s, social services have expanded greatly.

In the late 20th century the provision of better health service to all people at all ages became a goal at both private and governmental levels. The resulting rapid growth of health services and of the share they took of both personal and state income became of great concern to individual citizens as well as to policy makers. At the turn of the 21st century, health services employed about one-tenth of the workforce, and health care was increasingly available throughout the state. A significant development was that of hospitals specializing in orthopedic and mental care and the treatment of specific problems such as drug and alcohol abuse. Social services provided by the state include child protection, drug and alcohol rehabilitation, geriatric care, and help for victims of domestic violence.

The educational system is administered through public school districts that provide teachers, textbooks, laboratory materials, and physical equipment. Funds are secured from the state and local communities through taxes and bond issues. Private schools are largely supported by tuition. The state department of education establishes statewide standards for teacher certification and curricula and apportions money to the local school districts.

Pennsylvania has more than 100 four-year colleges and universities in addition to numerous two-year colleges. Philadelphia is a major centre of medical education, while Pittsburgh's Carnegie Mellon University—formed in 1967 by the merger of the Carnegie Institute of Technology (founded in 1900 as the Carnegie Technical School) and the Mellon Institute (1913)—makes that city a centre of science and engineering studies. Pennsylvania State University (or Penn State; 1855), in University Park, is the state land-grant (land-grant college) institution; it has many branch campuses throughout the state. Temple University (1884), in Philadelphia, the University of Pittsburgh (Pittsburgh, University of) (1787), and Lincoln University (1854) are also state-supported. There are also more than 50 private colleges and universities in Pennsylvania. Of these the University of Pennsylvania (Pennsylvania, University of) (1740), in Philadelphia, an Ivy League school, is one of the most distinguished. In 1765 it began the first institution for the study of medicine in the state. Today, the university's Wharton School is recognized for its leadership in business education, and its renowned Museum of Archaeology and Anthropology (also known as the Penn Museum) sponsors archaeological expeditions throughout the world.

Other schools with major reputations are Bryn Mawr College (1880), one of the Seven Sisters schools; Haverford College (1833) and Swarthmore College (1864), which are Quaker schools; and Villanova University (1842), a Roman Catholic institution—all near Philadelphia. Dating from the 18th century are Dickinson College (1773), in Carlisle; Franklin and Marshall College (1787), in Lancaster; and Washington and Jefferson College (1787), in Washington. Carlisle was the site of the Carlisle Indian Industrial School from 1879 to 1918; the facility became the home of the U.S. Army War College in 1951.

During colonial times Philadelphia was the focus of America's intellectual, cultural, and political life. As Pennsylvania grew and prospered, Pittsburgh and other, smaller cities also became centres of the arts, but Philadelphia remains in the national cultural spotlight.

Philadelphia is the home of one of the world's finest art collections, the Philadelphia Museum of Art (1877), as well as the Rodin Museum (1929). The Pennsylvania Academy of the Fine Arts (1805), also in Philadelphia, not only offers a base for teaching and study but also provides a notable collection of American art from the colonial through contemporary eras. The Carnegie Museum of Art (1895), in Pittsburgh, is noted for its holdings of American art and French Impressionist and Post-Impressionist paintings. The Palmer Museum of Art (1993), on the campus of Pennsylvania State University, has many fine contemporary paintings.

Pittsburgh and Philadelphia are well known for professional theatre. Two restored movie palaces form the centre of Pittsburgh's cultural district: Heinz Hall for the Performing Arts (the home of the Pittsburgh Symphony) and nearby Benedum Center for the Performing Arts (formerly the Stanley Theater). Philadelphia has dozens of theatre companies, among them the Walnut Street Theatre, said to be the oldest continually operating theatre in the country. The Wilma Theater creates original productions and develops local talent. Summer theatres have proliferated across the state, especially in the many resort areas. Penn State, Temple, and Carnegie Mellon universities offer major programs in theatre. The Pennsylvania Ballet gives performances within the state and also tours around the country.

Among well-known writers with Pennsylvania origins are Pearl Buck (Buck, Pearl), Rachel Carson (Carson, Rachel), James Michener (Michener, James), Christopher Morley (Morley, Christopher), John O'Hara (O'Hara, John), Mary Roberts Rinehart (Rinehart, Mary Roberts), John Updike (Updike, John), and Donald Barthelme (Barthelme, Donald).

Pennsylvania was the home of media pioneers. Benjamin Franklin (Franklin, Benjamin) was a major developer of newspapers and magazines. In the 20th century the Lippincott and Curtis (Curtis, Cyrus Hermann Kotzschmar) publishing families were noted for publishing books and magazines such as The Saturday Evening Post, Ladies Home Journal, and Country Gentleman. Andrew Carnegie (Carnegie, Andrew) of Pittsburgh was noted for the establishment of libraries throughout the country. The world's first commercial radio station, KDKA, began broadcasting in Pittsburgh in 1920.

At the time of European settlement, the Native American population was small and widely scattered. The Delaware, or Lenni Lenape, occupied the Delaware valley; the Susquehannock were in the lower Susquehanna River valley; the Erie and various groups of the Iroquois Confederacy— Seneca, Cayuga, Onondaga, and Oneida—were in northern Pennsylvania. Tribes of the Ohio River valley lived in the central and western parts of the state.

Swedes were the first European settlers in Pennsylvania. Traveling up the Delaware from a settlement at the present site of Wilmington, Del., Gov. Johan Printz (Printz, Johan Björnsson) of the colony of New Sweden established his capital on Tinicum Island (New Gothenborg) in 1643. Other Europeans, primarily the Dutch, established trading posts within Pennsylvania as early as 1647. A rivalry between the Dutch and the Swedes led Peter Stuyvesant (Stuyvesant, Peter), governor of New Netherland, to seize New Sweden in 1650. Dutch control of the region ended in 1664, when the English seized all of New Netherland in the name of the Duke of York (the future King James II).

William Penn intended that the colony provide a home for his fellow Quakers (members of the Society of Friends (Friends, Society of)). While still in England, he drew up the first of his “frames of government” and sent his cousin, William Markham, to establish a claim to the land and also to establish the boundaries of what became the city of Philadelphia. Penn arrived in 1682 and called a General Assembly to discuss the first Frame of Government and to adopt the Great Law, which guaranteed freedom of conscience in the colony. Under Penn's influence, fair treatment was accorded the Native Americans, who responded with friendship in return. When Penn returned to England in 1684, the new Quaker province had a firmly established government based on the people's will and religious tolerance.

For many Pennsylvanians, the period following these conflicts marked growing dissatisfaction with British rule. Limitations on westward expansion, especially as established by proclamation in 1763, were imposed to pacify the Indians, but Pennsylvanians pressed westward over the Allegheny Mountains. Outposts such as Fort Pitt (Fort Duquesne under the French; now Pittsburgh) became settlements vital to the flow of trade from the opening lands to the west.

In 1790 a new state constitution was adopted that replaced the unicameral legislature of the Revolutionary period with a bicameral one and a fairly strong governor. During the next 70 years, roads were improved and extended, canals were built, farm equipment was mechanized, and railroads spanned the state, all combining with the economic strength of the thrifty Philadelphians to make Pennsylvania a major commercial power. Beginning in 1820, important mining companies were formed to exploit Pennsylvania's deposits of hard and soft coal, and in 1859 Edwin L. Drake (Drake, Edwin Laurentine) drilled the world's first successful oil well at Titusville. During this same period the state became a leading producer of textiles, ships, lumber, tobacco, and, most important, iron and steel.

In both world wars, Pennsylvania's heavy industries were major suppliers of iron and steel, arms, and machinery. After World War II, however, the many changes taking place in the global economy began to affect Pennsylvania's emphasis on heavy industry. A relative decline in the state's manufacturing occurred between the mid-1960s and the mid-1980s, and Pennsylvania came to be identified as part of a “rust belt” in which former industrial economies fell victim to strong competition from overseas. The state's economy relied increasingly on a variety of high-technology industries and on the service sector.