SEPTA Route 10, also known as the Lancaster Avenue Line, to be known as T1 Lancaster Avenue Line, is a trolley line operated by the Southeastern Pennsylvania Transportation Authority (SEPTA) that connects the 13th Street station in Center City Philadelphia, Pennsylvania, to the 63rd Street–Malvern Avenue station in the Overbrook section of West Philadelphia. It is one out of five lines that is part of the SEPTA's subway–surface trolley system and is 11.6 mi (18.7 km) long. It is the least used subway-surface trolley line, but unlike Route 11, the most used subway-surface trolley line, it has overnight service.

West Philadelphia, nicknamed West Philly, is a section of the city of Philadelphia. Although there are no officially defined boundaries, it is generally considered to reach from the western shore of the Schuylkill River, to City Avenue to the northwest, Cobbs Creek to the southwest, and the SEPTA Media/Wawa Line to the south. An alternate definition includes all city land west of the Schuylkill; this would also include Southwest Philadelphia and its neighborhoods. The eastern side of West Philadelphia is also known as University City.