Pennsylvania Route 23 (PA 23) is a 81.04 mi (130.42 km) state highway in southeastern Pennsylvania. The route begins at Pennsylvania Route 441 in Marietta and heads east to U.S. Route 1 in Philadelphia.

PA 23 starts in Marietta, Pennsylvania, on the Susquehanna River, and proceeds east towards Lancaster, Pennsylvania as the Marietta Pike. West of Lancaster, Route 23 passes over US 30 (which here is an expressway parallel to Lincoln Highway), with the preceding Centerville Road and subsequent PA 741 providing complete access between 23 and 30. In downtown Lancaster, Route 23 splits onto the one-way Chestnut and Walnut Streets, with the latter also carrying PA 462 westbound. PA 462 eastbound is on King Street. In downtown Lancaster, PA 23 (and PA 462) crosses in succession: US 222/PA 272 southbound at Prince Street, PA 72 northbound at Queen Street, and US 222/PA 272 northbound at Lime Street. East of Lancaster, PA 23 passes beneath the stone arch Conestoga Creek Viaduct and crosses the Conestoga River before merging with US 30 for about 1/4 mile, forming a wrong-way concurrency and crossing the Conestoga a second time. After leaving US 30, it crosses the Conestoga a third time and heads east towards Morgantown, Pennsylvania.

In Morgantown, a grade-level intersection with Interstate 176 spur provides access to and from Reading only. PA 10 North connects 23 to a complete I-176 interchange which also gives access to the Pennsylvania Turnpike, I-76. East of Morgantown the route passes through the northern Chester County towns of Elverson, Warwick, South Coventry, and East Vincent before entering Phoenixville. In Phoenixville, PA 23 intersects PA 29 before continuing east to Valley Forge as Valley Forge Road. From here to its end, Route 23 generally follows the course of the Schuylkill River.

The Route passes through Valley Forge National Historical Park, the site where George Washington and his troops made an important winter encampment during the American Revolutionary War. At the east edge of the Park, 23 has a junction with US 422. East of Valley Forge the Route crosses north of King of Prussia through Upper Merion Township toward Bridgeport. Just before Bridgeport, 23 passes over the end of the never completed Schuylkill Parkway (23 Bypass) to 422. 23 then passes under DeKalb Pike US 202S.

Upon entering Bridgeport, 23 turns left on the Schuylkill Parkway. Traffic from 202 uses ramps built for the bypass to access 23 at this point. The Parkway ends in 1/4 mile and 23 becomes 4th Street in Bridgeport. At a light, 23 crosses US 202N. Exiting Bridgeport, 23 becomes Schuylkill River Road and passes under the bridge carrying I-276, the PA Turnpike's Philadelphia Extension, across the Schuylkill River. The Route then turns generally southward with the river and skirts a large quarry opposite. The Schuylkill River Road name ends as 23 passes under the I-476/Blue Route bridge across the Schuylkill River. Entering West Conshohocken, 23 becomes Front Street.

In West Conshohocken, Front Street intersects Matson Ford Road, which provides access to the I-476/I-76 interchange ramps which are signed for PA 23. Exiting West Conshohocken, Route 23 passes under I-76 and becomes Conshohocken State Road. The river swings away to the east and then to a parallel course while Conshohocken State Road continues through suburban Lower Merion Township toward Gladwyne and on to Bala Cynwyd. In Bala Cynwyd, 23 terminates at U.S. 1/City Avenue at the Philadelphia city boundary.

Until 1984, PA 23 continued east along Conshohocken State Road across US 1 to Belmont Avenue, where it was then aligned with Belmont Avenue until its terminus at U.S. Route 30/Girard Avenue. Mapquest still shows the Philadelphia County portion of Conshohocken State Road as 23 and the USGS Topographic map still has the Route 23 designation along Belmont Avenue.

In the 1960s plans were made to construct the Schuylkill Parkway between US Route 422 at the edge of Valley Forge Park and Bridgeport, along the Schuylkill River, to carry PA 23. Construction was started on the Bridgeport end in 1972, but stopped when PennDOT ran out of funds. Recently (c. 2006), traffic studies were funded along the current 23 alignment in Upper Merion Township to see if this bypass should be completed.

Construction started in February 2008 to reconstruct the interchange of PA 23 with US 422 westbound. The ramp from 422 west to 23 west was closed to eliminate the weave with traffic entering 422 west from 23 east. 422 west traffic for 23 west now exits on the current 23 east ramp to a new signal controlled intersection with 23 to turn left onto 23 west. The 23 east ramp onto 422 west was extended to become a third lane of 422 over the Schuylkill River to the Trooper Road/PA Route 363 exit. This is designed to help the weave that causes a major regional backup in the afternoon rush hour with traffic entering from 23 and traffic exiting 422 at 363.

In an effort to relieve existing and expected congestion, a proposed extension to be known as the "Lancaster-Norristown Expressway" began construction in 1976. Two years later, however, the project was canceled in response to local opposition concerned about the potential for increased traffic in the area. By the time the project was canceled, the roadway had been constructed in varying degrees: clearing, grading, pavement, culverts, a diamond interchange (with PA 772), and/or bridgework. As much of the alignment was graded but not paved, the natural terrain remains with the distinct drainage sloping of an expressway. The former planned alignment of the PA 23 freeway was given to local farmers to use. This appearance of the currently-abandoned alignment has given rise to the colloquial name: the "Goat Path" Expressway.