Pennsylvania becomes the second state to ratify the United States Constitution, five days after Delaware became the first.

The Constitution of the United States is the supreme law of the United States of America. It superseded the Articles of Confederation, the nation's first constitution. Originally comprising seven articles, it delineates the national frame of government. Its first three articles embody the doctrine of the separation of powers, whereby the federal government is divided into three branches: the legislative, consisting of the bicameral Congress (Article I); the executive, consisting of the president and subordinate officers (Article II); and the judicial, consisting of the Supreme Court and other federal courts (Article III). Article IV, Article V, and Article VI embody concepts of federalism, describing the rights and responsibilities of state governments, the states in relationship to the federal government, and the shared process of constitutional amendment. Article VII establishes the procedure subsequently used by the 13 States to ratify it. It is regarded as the oldest written and codified national constitution in force.Since the Constitution came into force in 1789, it has been amended 27 times, including one amendment that repealed a previous one, in order to meet the needs of a nation that has profoundly changed since the 18th century. In general, the first ten amendments, known collectively as the Bill of Rights, offer specific protections of individual liberty and justice and place restrictions on the powers of government. The majority of the 17 later amendments expand individual civil rights protections. Others address issues related to federal authority or modify government processes and procedures. Amendments to the United States Constitution, unlike ones made to many constitutions worldwide, are appended to the document. The original U.S. Constitution was written on four pages of parchment.According to the United States Senate: "The Constitution's first three wordsWe the Peopleaffirm that the government of the United States exists to serve its citizens. For over two centuries the Constitution has remained in force because its framers wisely separated and balanced governmental powers to safeguard the interests of majority rule and minority rights, of liberty and equality, and of the federal and state governments." The first permanent constitution, it is interpreted, supplemented, and implemented by a large body of federal constitutional law, and has influenced the constitutions of other nations.

Pennsylvania ( (listen) PEN-səl-VAY-nee-ə; Pennsylvania German: Pennsilfaani), officially the Commonwealth of Pennsylvania, is a U.S. state spanning the Mid-Atlantic, Northeastern, and Appalachian regions of the United States. It borders Delaware to the southeast, Maryland to the south, West Virginia to the southwest, Ohio to the west, Lake Erie and the Canadian province of Ontario to the northwest, New York to the north, and New Jersey to the east.

Of the 50 U.S. states, Pennsylvania is the 33rd-largest by area and the fifth-most populous, with over 13 million residents as of 2020; it ranks ninth in population density. Nearly half the population is concentrated in the southeastern Delaware Valley, centered around the state's largest city, Philadelphia (6.25 million); another one-third live in Greater Pittsburgh (2.37 million) in the southwest. The state capital and 15th-largest city is Harrisburg; other major cities include Allentown, Scranton, Lancaster, and Erie.

Pennsylvania's geography is highly diverse: the Appalachian Mountains run through its center, while the Allegheny and Pocono Mountains span much of the northeast; close to 60% of the state is forested. While it has only 140 miles (225 km) of waterfront along Lake Erie and the Delaware River, Pennsylvania has more navigable rivers than any other state, including the Delaware, Ohio, and Pine Creek.

Pennsylvania's was one of the thirteen British colonies that would eventually form the United States. It was founded in 1681 through royal land grant to William Penn, son of the state's namesake; the southeast portion was once part of the colony of New Sweden. Established as a haven for religious and political tolerance, the Province of Pennsylvania was noteworthy for its relatively peaceful relations with native tribes, innovative government system, and religious pluralism. Pennsylvania's governing framework inspired the U.S. Constitution, which, along with the Declaration of Independence, was drafted in Independence Hall in Philadelphia; the city also hosted the first and second Constitutional Convention that led the American Revolution. Pennsylvania became the second state to ratify the Constitution on December 12, 1787.