Pennsylvania Route 309 (PA 309) is a major highway which runs for 134 miles (216 km) through Pennsylvania in the United States. It connects Philadelphia and its northern suburbs to Allentown, Hazleton, and Wilkes-Barre. A limited-access highway portion of PA 309 in the Wilkes-Barre area is known as the North Cross Valley Expressway. A limited-access highway portion of PA 309 in Montgomery County is known as the Fort Washington Expressway.

The highway runs from northern Philadelphia through the Lehigh Valley, the Poconos, and Wilkes-Barre to Bowman Creek, a village in Noxen Township, Wyoming County. It parallels the newer Interstates 476 and 81 for much of its length.

PA 309 begins in the East Oak Lane section of Philadelphia at Old York Rd (Pennsylvania Route 611). It follows Cheltenham Avenue and Ogontz Avenue for a short distance north to become the Fort Washington Expressway, a freeway that forms a major commuter route through the northern suburbs of Philadelphia, passing north through the towns of Fort Washington and Ambler, interchanging with the mainline of the Pennsylvania Turnpike near the former. At Montgomeryville, the route becomes Bethlehem Pike, a four-lane highway through Montgomeryville, Telford, Quakertown, and Coopersburg, with alternating arterial road and freeway segments known for large sections of suburban sprawl. North of Coopersburg, the freeway briefly merges with Interstate 78 to form a primarily six-lane highway that crosses South Mountain before cutting through Allentown's South Side and skirting the city's southwest border.

After I-78 and PA 309 split near Allentown's southwestern corner, the PA 309 freeway continues north, interchanging with U.S. Route 22 just east of Interstate 476. The freeway then empties onto a two-lane road northwest of Allentown, which is being widened to four lanes as of July 2008 in the Schnecksville area. It continues north through the Lehigh County suburbs of Orefield, Schnecksville, and New Tripoli then turns northwest, crossing Blue Mountain and the Appalachian Trail on the way to Tamaqua. It then parallels Interstate 81 northward, running through downtown Hazleton and meeting with Interstate 80 north of the city. North of I-80, the route climbs Nescopeck Mountain to the town of Mountain Top, then descends Penobscot Mountain into the Wyoming Valley and merges onto Interstate 81.

After running concurrently with Interstate 81 for several miles, PA 309 exits onto the North Cross Valley Expressway, a freeway through Wilkes-Barre and across the Susquehanna River to Trucksville. The route then continues northward as an arterial through Shavertown and Dallas, to its end at PA Route 29 at Bowman Creek, south of Tunkhannock.

Starting out as a Native American path now referred to as the "Minsi Trail", this route became part of the Bethlehem Pike. In 1926, the U.S. Route 309 designation was given to a route that consisted of Stenton Avenue in Philadelphia, Bethlehem Pike (Old Route 309) from the Philadelphia line to Spring House, modern-day PA 309 into Bucks County, Bethlehem Pike (Old Route 309) through Sellersville, modern-day PA 309 from Quakertown to Lanark, and modern-day PA 145 to Allentown; various city streets through Allentown, exiting northward on Walbert Avenue; modern-day PA 309 from Walbert (in South Whitehall Township) to Schnecksville, modern-day PA 873 to Weiders Crossing near Lehigh Gap, modern-day PA 248 to Weissport, modern-day US 209 to Nesquehoning, modern-day PA 93 to Hazleton, and modern-day PA 309 (and PA 309 Business) to Wilkes-Barre.

In 1930 the highway was extended to the New York state line, following River Street to Pittston, modern-day PA 92 to Tunkhannock, modern-day US 6 to Towanda, and modern-day US 220 to South Waverly. In 1946 the route between Wilkes-Barre and Tunkhannock was changed to the modern-day PA 309 alignment from Wilkes-Barre to Bowman Creek and modern-day PA 29 to Tunkhannock.

In 1954 the routing between Allentown and Hazleton was completely changed. US 309 was routed north on modern-day PA 145 to Fullerton, then west on the Lehigh Valley Thruway along with the rerouted US 22 to Fogelsville. US 309 then turned north on modern-day PA 100 up to Pleasant Corners, and then followed modern-day PA 309 to Hazleton.

The late 1950s saw the beginnings of bypasses on the route. North of Philadelphia, the Fort Washington Expressway from the PA 73 interchange to north of Spring House opened in 1959; the rest of that expressway from PA 73 south to PA 152 opened in 1961. A bypass west of Allentown from Lanark to US 22 north of Cetronia was completed in 1959, and extended to Walbert in 1962 when US 309 was placed on modern-day PA 309 from US 22 to Pleasant Corners. US 309 had now completely replaced the stretch of the 1920s-era Pennsylvania Route 22 between the former PA 3 in Allentown and the former PA 19 in Wilkes-Barre.

The north end of US 309 had always been shared with other U.S. highways (6 and 220). In 1964 the US 309 designation was removed from those shared sections, leaving the northern terminus at Tunkhannock. In 1967, work began on an expressway to bypass Sellersville from just north of the Montgomery/Bucks County line to just south of Quakertown. This bypass opened in 1969. By that time, US 309 was no more; it was decommissioned in 1968 and was replaced by PA 309 south of Bowman Creek and by PA 29 from Bowman Creek to Tunkhannock.

Pennsylvania Route 309 Business, often referred to as Business Route 309 or PA 309 BR, is the original alignment of PA Route 309 before the road was realigned to run concurrent with Interstate 81 between Exits 165 and 170. This business route stretches approximately 4.7 miles (7.6 km) through Wilkes-Barre Township.

Where PA 309 merges onto Interstate 81 at Exit 165, Business Route 309 heads north on Wilkes-Barre Township Boulevard. The route intersects with main streets such as Blackman Street, East Northampton Street, Highland Park Boulevard, Coal Street, Mundy Street, and Scott Street. It then follows along Kidder Street where it forms the northern boundary of the Wyoming Valley Mall property and rejoins PA 309 at the intersection of PA Route 315 near Exit 170 of Interstate 81.

At the intersection of Business Route 309 and Casey Avenue is a park and ride facility with 75 total spaces.