The Constitutional Convention took place in Philadelphia from May 25 to September 17, 1787. Although the convention was intended to revise the league of states and first system of government under the Articles of Confederation, the intention from the outset of many of its proponents, chief among them James Madison of Virginia and Alexander Hamilton of New York, was to create a new Frame of Government rather than fix the existing one. The delegates elected George Washington of Virginia, former commanding general of the Continental Army in the late American Revolutionary War (17751783) and proponent of a stronger national government, to become President of the convention. The result of the convention was the creation of the Constitution of the United States, placing the Convention among the most significant events in American history.

The convention took place in the old Pennsylvania State House (now known as Independence Hall) in Philadelphia. At the time, the convention was not referred to as a constitutional convention. It was contemporarily known as the Federal Convention, the Philadelphia Convention, or the Grand Convention at Philadelphia. Nor did most of the delegates arrive intending to draft a new constitution. Many assumed that the purpose of the convention was to discuss and draft improvements to the existing Articles of Confederation, and would not have agreed to participate otherwise. Once the convention began, however, most of the delegates though not all came to agree in general terms that the goal would be a new system of government, not simply a revised version of the Articles of Confederation.

Several broad outlines were proposed and debated, most notably James Madison's Virginia Plan and William Paterson's New Jersey Plan. The Virginia Plan was selected as the basis for the new government, and the delegates quickly reached consensus on a general blueprint of a federal government with three branches (legislative, executive, and judicial) along with the basic role of each branch. However, disagreement over the specific design and powers of the branches delayed progress for weeks and threatened the success of the convention. The most contentious disputes involved the legislature, specifically the composition and election procedures for the Senate as the upper legislative house of a bicameral Congress; and whether proportional representation was to be defined by a state's geography or by its population. The role of the executive was also hotly debated, including the key issues of whether to divide the executive power among three people or vest the power in a single chief executive to be called the President; how a president would be elected; the length of a presidential term and the number of allowable terms; what offenses should be impeachable; and whether judges should be chosen by the legislature or the executive. Finally, slavery was also a contentious issue, with the delegates debating the insertion of a fugitive slave clause; whether to allow the abolition of the slave trade; and whether slaves were to be counted in proportional representation. Most of the time during the convention was spent on deciding these issues.

Progress was slow until mid-July, when the Connecticut Compromise resolved enough lingering arguments for a draft written by the Committee of Detail to gain acceptance. Though more modifications and compromises were made over the following weeks, most of this draft can be found in the finished version of the Constitution. After several more issues were debated and resolved, the Committee of Style produced the final version in early September. It was voted on by the delegates, inscribed on parchment with engraving for printing, and signed by thirty-nine of fifty-five delegates on September 17, 1787. The completed proposed Constitution was printed in several copies for review which began the debates and ratification process. Soon after it was also printed in newspapers for public review.

Philadelphia is the largest city in the Commonwealth of Pennsylvania in the United States. It is the sixth-most-populous city in the United States and the most populous city in the state of Pennsylvania, with a 2020 population of 1,603,797. It is the second-most populous city in the Northeastern United States, behind New York City. Since 1854, the city has had the same geographic boundaries as Philadelphia County, the most-populous county in Pennsylvania and the urban core of the eighth-largest U.S. metropolitan statistical area, with more than 6 million residents as of 2017. Philadelphia is the economic and cultural center of the greater Delaware Valley along the lower Delaware and Schuylkill rivers within the Northeast megalopolis. The Delaware Valley's 2019 estimated population of 7.21 million makes it the ninth-largest combined statistical area in the United States.Philadelphia is one of the oldest municipalities in the United States. William Penn, an English Quaker, founded the city in 1682 to serve as capital of the Pennsylvania Colony. Philadelphia played an instrumental role in the American Revolution as a meeting place for the Founding Fathers of the United States, who signed the Declaration of Independence in 1776 at the Second Continental Congress, and the Constitution at the Philadelphia Convention of 1787. Several other key events occurred in Philadelphia during the Revolutionary War, including the First Continental Congress, the preservation of the Liberty Bell, the Battle of Germantown, and the Siege of Fort Mifflin. Philadelphia remained the nation's largest city until 1790, when it was surpassed by New York City. It served as one of the nation's capitals during the revolution, and served as temporary U.S. capital while Washington, D.C. was under construction.

In the 19th and 20th centuries, Philadelphia became a major industrial center and a railroad hub. Its industrial jobs attracted European immigrants, most of whom initially came from Ireland and Germany—the two largest reported ancestry groups in the city as of 2015. Later immigrant groups in the 20th century came from Italy (Italian being the third-largest European ethnic ancestry currently reported in Philadelphia) and other Southern European and Eastern European countries. In the early 20th century, Philadelphia became a prime destination for African Americans during the Great Migration after the Civil War. Puerto Ricans began moving to the city in large numbers in the period between World War I and II, and in even greater numbers in the post-war period. The city's population doubled from one million to two million people between 1890 and 1950.

The Philadelphia area's many universities and colleges make it a top study destination, as the city has developed as an educational and economic hub. As of 2019, the Philadelphia metropolitan area is estimated to produce a gross metropolitan product (GMP) of $490 billion. Philadelphia is the center of economic activity in Pennsylvania and is home to five Fortune 1000 companies. The Philadelphia skyline is expanding, with a market of almost 81,900 commercial properties in 2016, including several nationally prominent skyscrapers. Philadelphia has more outdoor sculptures and murals than any other American city. Fairmount Park, when combined with the adjacent Wissahickon Valley Park in the same watershed, is one of the largest contiguous urban park areas in the United States. The city is known for its arts, culture, cuisine, and colonial history, attracting 42 million domestic tourists in 2016 who spent $6.8 billion, generating an estimated $11 billion in total economic impact in the city and surrounding four counties of Pennsylvania. Philadelphia is also a biotechnology hub.Philadelphia is the home of many U.S. firsts, including the nation's first library (1731), hospital (1751), medical school (1765), national capital (1774), university (by some accounts) (1779), stock exchange (1790), zoo (1874), and business school (1881). Philadelphia contains 67 National Historic Landmarks and the World Heritage Site of Independence Hall. The city became a member of the Organization of World Heritage Cities in 2015, as the first World Heritage City in the United States.