The flag of the Commonwealth of Pennsylvania consists of a blue field on which the state coat of arms is embroidered. Originally authorized by the state in 1799, the current design was enacted by law in 1907. The blue field must, by legislative mandate, match the shade of blue in the US flag (Pantone 282c).
The state coat of arms is surrounded by draft horses on both sides, and a bald eagle, which represents Pennsylvania's loyalty to the United States, above. The state coat of arms includes a ship under full sail, a plow, and three sheaves of wheat indicating the significance of commerce, labor, perseverance and agriculture to the state. Surrounding the coat of arms is a stalk of Indian corn on the left and an olive branch on the right. These represent the state's recognition of its past and its hope for the future. The scroll below the coat of arms reads: "Virtue, Liberty and Independence," which is the state's motto.
In the summer of 2007, a bill was introduced to the state legislature to add "Pennsylvania" to the bottom of the flag in golden letters. The Pennsylvania House of Representatives voted in favor of the change. The legislation was proposed by State Representative Tim Solobay. The Senate has not yet taken action on the bill.
Proposed Pennsylvania flag - pointing to the future
PA Flag Proposal "PixieCoeFeets"
Pennsylvania flag proposal 1 by Hans. Dec 2013. (details)
Pennsylvania flag proposal 2 by Hans. Dec 2013. (details)
Proposed PA State Flag with Bloody Bucket by Cwalt925
PA State Flag inspired after Texas, by Cwalt925
PA flag proposal by 5thEye
PA flag proposal by 5thEye (yellow version)
PA flag proposal by nhprman
Keystone Tricolor by Tara Stark
Blue Keystone with White in hoist (matched to white tech stripe) and gold ib fly to perform well in a good breeze. Design by Rotten Ali.
PA flag proposal by Gutberg
Pennsylvania state flag proposed by Ken Morton. Simple is best.
PA state flag proposal #1 by Jeff Cook
PA state flag proposal #2 by Jeff Cook
Result sheet from the PA study of June 2019. Great winner - Keystone in COA colors by Tara Stark.
The horizontal color bars come from the Pennsylvania coat of arms: blue with a a ship carrying state commerce to all parts of the world; yellow with a clay-red plough, a symbol of Pennsylvania's rich natural resources; and green with three golden sheaves of wheat, representing fertile fields and Pennsylvania's wealth of human thought and action. The center symbol is a keystone, referring historically to Pennsylvania’s central location along the arch of the 13 original states, as well as the state’s vital role in holding together the states of the newly formed Union. Posted by Preston Knapp 
Pennsylvania received the nickname "The Keystone State" in reference to its importance in early American history. It was located in the center of the original thirteen states, between the North and the South. Many documents, like the United States Declaration of Independence, were signed in the state. The state was also an economical "keystone", concentrating both industry, like northern states, and agriculture, like southern states. The keystone currently appears in all kinds of official imagery, such as road signs, car license plates, the government website, logos of government departments, and the state quarter. It is central to many flag proposals as well. In some designs, it's substituted by keys.
William Penn was the founder of the Province of Pennsylvania, which became the current Commonwealth of Pennsylvania in 1783. During his government, the city of Philadelphia was planned and developed. Moreover, he was an early champion of democracy and religious freedom.
In his honor, Pennsylvania received the "Quaker State" nickname, in reference to Penn's belonging in the quaker movement.
Penn family's coat of arms can be blazoned as "argent, on a fess sable three plates", i.e., white with three white circles on a black horizontal stripe.