At the top of the list of tallest buildings in Philadelphia is the 60-story Comcast Technology Center, which topped out at 1,121 feet (342 m) in Center City on November 27, 2017 and was completed in 2018. Comcast Technology Center is the tallest building outside lower Manhattan and Chicago, and is the tenth-tallest building in the United States, as of 2019 . Philadelphia is home to more than 300 completed high-rise buildings up to 330 feet (100 m), and 56 completed skyscrapers of 330 feet (100 m) or taller, of which 31 are 400 feet (122 m) or taller.
The second-tallest building in Philadelphia is the 58-story Comcast Center at 974 feet (297 m), while the third-tallest building is One Liberty Place, which rises 61 floors and 945 feet (288 m). One Liberty Place stood as the tallest building in Pennsylvania for over 20 years until the completion of Comcast Center in 2008. Overall, seven of the ten tallest buildings in Pennsylvania are in Philadelphia, with the remainder being in Pittsburgh. Philadelphia is one of only five American cities with two or more completed buildings over 900 feet (270 m) tall, the others being New York City, Chicago, Houston, and Los Angeles.
Philadelphia's history of tall buildings is generally thought to have begun with the 1754 addition of the steeple to Christ Church, which was one of America's first high-rise structures. Through most of the 20th century, a "gentlemen's agreement" prevented buildings from rising higher than the 548-ft (167-m) Philadelphia City Hall. The completion of One Liberty Place in 1987 broke the agreement, and Philadelphia has since seen the construction of ten skyscrapers that eclipse City Hall in height.
Philadelphia has twice held the tallest habitable building in North America, first with Christ Church, then with City Hall. The latter reigned as the world's tallest building from 1894 to 1908, and is currently the world's second-tallest masonry building, only 1.6 feet (0.49 m) shorter than Mole Antonelliana in Turin. Like other large American cities, Philadelphia went through a massive building boom in the 1970s and 1980s, resulting in the completion of 20 skyscrapers of 330 feet (100 m) or taller.