As a prominent Quaker leader and the founder of Pennsylvania, William Penn is an important figure in religious and political history. He worked to bring religious freedom and tolerance to his native Britain, and when Pennsylvania was established as the last of the restoration colonies, he sought to graft these principles to the American experience. The colony's constitution, which Penn helped to compose, served as a model for the U.S. Constitution. Pennsylvania's democratic heritage was strengthened further when Penn made a peace treaty with the Native Americans who lived in the colony. Voltaire, a French philosopher, noted that the document was the only treaty with Native Americans that was "never sworn to and never broken." Neither the Quakers nor the Native Americans saw any need to swear to their word. Penn's vision extended to the international realm. More than two hundred years ahead of his time, he advocated a league of nations to maintain world peace.

Penn's life makes an exciting story. Born into the British establishment, Penn alienated his father, a famous admiral, by joining the Quaker movement, whose members were persecuted in seventeenth-century England. Penn was imprisoned several times for his religious beliefs. He was also incarcerated for failing to pay off a debt that was incurred to finance his colony. Despite his notoriety as a spokesman for a persecuted minority, Penn remained on cordial terms with King Charles II, who granted him the charter to found Pennsylvania; with the Duke of York, later King James II; and with the diarist Samuel Pepys, who was openly critical of Quakerism. Penn headed several estates, married twice, and raised a family. Although he was expelled from college as a young man, he developed an intellectual nature. He wrote numerous books and pamphlets, and devised the city plan for Philadelphia.

Penn offers a history not merely of an individual, but of a movement. Historically, Quakers have exercised an influence far greater, proportionally, than their small numbers would suggest. They have worked for social reform, founding good schools, spreading humanitarian ideals, and teaching peace and tolerance by example. The Quaker belief that "there is that of God in everyone" implies that human life is sacred and that all people should be treated equally.