Pennsylvania Route 34 (PA 34) is a 62-mile (100 km) long state route located in southern Pennsylvania. The southern terminus of the route is at U.S. Route 15 Business in Gettysburg. The northern terminus is at U.S. Route 11 and U.S. Route 15 south of Liverpool.

PA 34 intersects Interstate 81, US 11, U.S. Route 322, and U.S. Route 22.

PA 34 begins at an intersection with US 15 Business in Gettysburg, Adams County, with the road continuing south as part of US 15 Business. From here, the route heads north on two-lane undivided Carlisle Street past homes. PA 34 crosses into Cumberland Township and becomes Biglerville Road, passing through fields within Gettysburg National Military Park. After leaving the park boundaries, the road heads through rural areas with residential and commercial development. The route heads into Butler Township and crosses the Gettysburg and Northern Railroad as it passes through a mix of farms and woods with some homes. PA 34 runs through more rural areas with occasional development before crossing into Biglerville and becoming South Main Street, passing residences and a few businesses as it intersects PA 394. The route continues into the downtown area and comes to a junction with PA 234. Here, the road becomes North Main Street and passes more homes before heading back into Butler Township.

At this point, PA 34 becomes Carlisle Road and comes into open farmland with occasional residences. The route enters Menallen Township and runs through Floradale prior to curving to the northeast through more agricultural areas with some patches of woods and homes. The road passes through a small corner of Bendersville before heading through more rural areas of Menallen Township. PA 34 heads into Tyrone Township and passes under the Gettysburg and Northern Railroad before making a turn to the north. The route crosses the Bermudian Creek into Huntington Township and runs through Idaville before heading through more areas of farms, woods, and residences.

PA 34 crosses into Dickinson Township in Cumberland County and runs through more agricultural areas with some homes, passing through Goodyear. The road continues north and passes through Hunters Run before entering South Middleton Township and crosses forested South Mountain, running a short distance to the east of the Gettysburg and Northern Railroad as it heads northeast. The route heads into Mount Holly Springs and becomes Yates Street, running through wooded areas of homes before intersecting the northern terminus of PA 94. At this point, PA 34 turns north onto South Baltimore Avenue and turns northwest, crossing the Gettysburg and Northern Railroad before passing through more forests. The road heads into residential and commercial areas, turning north to become North Baltimore Avenue. The route passes under a Norfolk Southern railroad line before crossing back into South Middleton Township and becoming Holly Pike, passing a few residential subdivisions before heading into a mix of farmland and woodland with a few homes. PA 34 crosses PA 174 and runs through more agricultural areas with some residential and commercial development. Development increases as the road passes through Bonny Brook and becomes the border between Carlisle to the west and South Middleton Township to the east a short distance later, becoming South Hanover Street. The route widens into a four-lane divided highway and fully enters Carlisle as it interchanges with I-81 in a commercial area.

Past this interchange, PA 34 becomes a four-lane undivided road and passes several homes. The route heads into the commercial downtown of Carlisle and comes to an intersection with US 11/PA 74/PA 641. At this point, US 11 turns north to join PA 34 on North Hanover Street, narrowing to two lanes and turning northeast past more homes and businesses. At a Norfolk Southern railroad crossing, PA 34 splits from US 11 by turning north onto Carlisle Springs Road and passes through industrial areas before running past residential neighborhoods. The route crosses into North Middleton Township and passes under I-76 (Pennsylvania Turnpike), becoming Spring Road and curving northeast past a few businesses. The road turns to the north again and runs through residential areas with a few businesses, crossing the Conodoguinet Creek and turning northeast past more development. PA 34 heads into Middlesex Township and runs through more rural areas of homes, coming to an intersection with PA 944. At this point, PA 944 joins PA 34, passing through the community of Carlisle Springs, where PA 944 turns to the east. PA 34 runs northeast through open farmland before entering wooded areas of homes, at which point the route ascends forested Blue Mountain.

At the summit of the mountain, PA 34 turns northwest and heads into Carroll Township in Perry County, where it descends Blue Mountain and passes a few homes. The road turns north and crosses Little Mountain before coming into a mix of farms and woods with some residential and commercial development. The route curves to the northwest and reaches an intersection with PA 850 in Shermans Dale. At this junction, PA 850 turns northwest to join PA 34, and the road continues past a few businesses before crossing Sherman Creek and passing a mix of farmland and residences as it runs to the east of the creek. The road continues through more farm fields and woods with homes and reaches the community of Dromgold, where PA 850 splits to the west and PA 34 turns to the northeast. The road runs through the community of Crums Corners before coming to a junction with PA 274 in Mecks Corner. Here, PA 34 turns northwest to join PA 274, becoming the border between Carroll Township to the west and Wheatfield Township to the east, heading through forests before continuing into agricultural areas with a few homes. The road heads into Centre Township and winds northwest through farms, woods, and residences before coming into New Bloomfield. PA 34/PA 274 turns north onto South Carlisle Street and passes homes before coming to a circle the center of town. At this point, PA 274 splits to the west and PA 34 turns east onto East Main Street, running past more residences.

The route turns northeast and heads back into Centre Township, becoming Keystone Way and passes through agricultural areas with some homes. The road heads into a mix of farmland, woodland, and residences as it winds northeast and enters Oliver Township. Here, PA 34 curves north across forested Limestone Ridge prior to heading northeast again and passing through farmland and woodland with some homes and businesses. The route runs through Buffalo Bridge and reaches an intersection with PA 849. Here, PA 849 turns north to join PA 34, heading through more rural areas before crossing into Newport. The two routes turn northwest onto South 4th Street, passing homes. PA 34 splits from PA 849 by turning northeast onto Market Street and passing through the commercial downtown. The route passes under a Norfolk Southern railroad line prior to crossing the Juniata River into Howe Township. At this point, the road becomes Red Hill Road and runs through agricultural and wooded areas with some development. PA 34 comes to an interchange with the US 22/US 322 freeway and continues through more farmland with some homes. The route turns north to cross forested Berry Mountain and curves east-northeast to run through forests in between Buffalo Mountain to the north and Berry Mountain to the south, heading into Buffalo Township and becoming Hunters Valley Road. Farther east, the road heads through a mix of farmland and woodland with some homes. PA 34 curves south and then east to reach its northern terminus at US 11/US 15 just west of the Millersburg Ferry across the Susquehanna River.