Since its founding, the only colony that practiced religious tolerance has attracted a wide diversity of religious sects. Founder William Penn was a Quaker and many other Quakers followed him to the new city to escape English persecution. Their influence can be seen in the many Quaker Friends’ schools and meeting houses that still exist.

Today, Christianity is the dominant religion in the city, with Protestants and Roman Catholics making up the two largest sects in similar numbers. There is a significant Eastern Orthodox population, and since the early 1800s, there has been a large Jewish population that has continued to grow as Eastern European Jews have immigrated to Philadelphia. Many of the Jewish communities left the city for the suburbs during the period 1950–2000, and some synagogues were converted to mosques and Baptist churches.

Smaller religious groups include Islam and Hinduism, with an increase in immigration from the Middle East, Pakistan, Bangladesh, and India. There is also a small Muslim community, about 85 percent of which is African American.