The Philadelphia trolleybus system forms part of the public transportation network serving Philadelphia, in the state of Pennsylvania, United States. It opened on October 14, 1923, and is now the second-longest-lived trolleybus system in the world. One of only four such systems currently operating in the U.S., it presently comprises three lines and is operated by the Southeastern Pennsylvania Transportation Authority (SEPTA), with a fleet of 38 trolleybuses, or trackless trolleys as SEPTA calls them. The three surviving routes serve North and Northeast Philadelphia and connect with SEPTA's Market–Frankford rapid transit line.

The Philadelphia Transportation Company (PTC) was the main public transit operator in Philadelphia, Pennsylvania, from 1940 to 1968. A private company, PTC was the successor to the Philadelphia Rapid Transit Company (PRT), in operation since 1902, and was the immediate predecessor of the Southeastern Pennsylvania Transportation Authority (SEPTA).