Pennsylvania Route 73 (PA 73) is a 62.51 miles (100.60 km) long east–west state highway in southeastern Pennsylvania. It runs from Pennsylvania Route 61 in Leesport to the New Jersey state line on the Tacony-Palmyra Bridge in Philadelphia, where it continues as New Jersey Route 73.

Predating the Interstate and U.S. Highway Systems, the Skippack Pike, a modern section of the route, served as the primary connector between Philadelphia and the northwest suburbs.

PA 73 begins at an intersection with Pennsylvania Route 61 in Leesport, north of Reading. It runs east along the shore of Lake Ontelaunee, intersecting U.S. Route 222 in Maiden Creek. Southeast of Maiden Creek, the route runs southeast, traversing a small mountainous region of the county. PA 73 intersects with Pennsylvania Route 12 near Pricetown and Pennsylvania Route 662 in Oley. It enters Boyertown as Philadelphia Avenue, meeting the eastern terminus of Pennsylvania Route 562 in the middle of town, and entering Montgomery County at the Boyertown-Gilbertsville border.

East of the county border, PA 73 interchanges with Pennsylvania Route 100, then continues southeast through Gilbertsville. In contrast to the mountainous Berks County terrain of 73, the elevation in Montgomery is much less, ranging from 100 feet (30 m) to 350 feet (106 m) above sea level. It then heads east as Big Road, where Pennsylvania Route 663 briefly joins the route from the south before leaving again on its own alignment. PA 73 continues southeast through Frederick and Zieglerville, where it joins with Pennsylvania Route 29 to head south on Gravel Pike, paralleling the Perkiomen Creek and Perkiomen Trail. The road turns into Main Street through central Schwenksville. PA 73 leaves for its own alignment, known as Skippack Pike, south of Schwenksville, crossing the Skippack Creek before heading southeast once again, entering the outer suburbs of Philadelphia.

The route continues past Graterford Prison, entering central Skippack, where it meets Pennsylvania Route 113. It briefly crosses Evansburg State Park, intersecting Bustard Road which provides access to Interstate 476 before heading through Worcester Township, where it intersects Pennsylvania Route 363. It passes under Interstate 476 without a direct interchange before entering Blue Bell, where it intersects with U.S. Route 202. It continues southeast through Blue Bell, passing Fort Washington State Park before crossing the Wissahickon Creek, and turning south onto Bethlehem Pike for a brief distance before again turning east onto Church Road.

PA 73 continues east through the densely populated northern Philadelphia suburbs, interchanging with the Fort Washington Expressway in Springfield, and with Pennsylvania Route 152 in Glenside. It briefly turns northwest onto Washington Lane before heading southeast again onto Township Line Road, which forms the boundary between Cheltenham and Abington townships. It intersects with Pennsylvania Route 611 before entering the city of Philadelphia.

The road continues as Cottman Avenue through Northeast Philadelphia, meeting Pennsylvania Route 232 at an intersection locally known as the Five Points. Passing through the Lawncrest and Rhawnhurst neighborhoods, it intersects Roosevelt Boulevard (US 1) at a massive interchange near Pennypack Park with PA 73 intersecting the outer six lanes of the Boulevard while the inner six pass under Cottman. It continues through the Mayfair neighborhood, meeting U.S. Route 13 on Frankford Avenue. It then briefly operates as a one-way pair along Torresdale and Princeton Avenues and State Road and Cottman Avenue, before interchanging with Interstate 95 and turning southwest onto New State Road. This road turns into a traffic circle at the foot of the Tacony-Palmyra Bridge; PA 73 traverses the circle and crosses the bridge into New Jersey, where it continues as New Jersey Route 73.

The Skippack Pike, a portion of PA 73 between Skippack and Bethlehem Pike in Whitemarsh, dates back to 1713, when settlers in Skippack petitioned Philadelphia officials for a road to their community for purposes of hauling grain to the mill in Whitemarsh. During the American Revolutionary War, George Washington's army suffered a defeat at the Battle of Germantown on October 4, 1777 and had to encamp along the Pike until October 8. The Americans later marched east on the road while preparing for a counterattack at the Battle of White Marsh.

The Skippack Turnpike Company was incorporated in 1845 to construct a turnpike from Whitemarsh to Skippack but the project was abandoned after several efforts. In 1853, a second charter was granted and the turnpike was completed in 1855 near Worcester Township.

When the state began maintenance over roads via the Sproul Road Bill (signed May 31, 1911), the system did not include the direct Reading–Philadelphia routes that PA 73 and U.S. Route 422 are today. PA 73 was adopted as Legislative Route 197, the main route that connected Philadelphia and its northwest suburbs. Legislative Routes paved the way for Pennsylvania's first Traffic Routes in 1924 and a new set of routes, including PA 73, that were added in the late 1920s.

In the original 1928 routing, PA 73 deviated from its current route west of Manatawny to follow Hoch Road, Bertolet Mill Road, and Main Street in the hamlet of Oley. The route then turned south to leave the hamlet on what is now Friedensburg Road to Reading and continued south along the current Pennsylvania Route 625 routing to end at Pennsylvania Route 23 near Blue Ball. The highway entered the city of Reading from the south as the New Holland Road, Lancaster Avenue and Bingaman Street into downtown Reading, concurrent with U.S. Routes 122 and 222. North of the Schuylkill River crossing, PA 73 turned east to overlap U.S. Route 422 along Perkiomen Avenue. East of the city in Mount Penn, PA 73 followed Friedensburg Road to Oley. The current segment from Oley to Leesport was designated as Pennsylvania Route 383.

PA 73 originally ended at Roosevelt Boulevard (US 1) in Northeast Philadelphia. After the Tacony-Palmyra Bridge was built in 1929, the eastern terminus was moved to its current location on the bridge at the New Jersey state line. It followed Cottman Avenue, Frankford Avenue, and Levick Street into the bridge. By 1966, the western terminus was moved to its current location in Leesport.