Pennsylvania Route 18 (PA 18) is a major north–south highway in Western Pennsylvania whose southern terminus is at West Virginia Route 69 at the state line in Greene County, Pennsylvania near the village of Garrison, while the northern terminus is at PA Route 5 in Lake City, Pennsylvania. At a length of , PA 18 is one of the few state routes in Pennsylvania — north–south or east–west — to traverse the entire state. It also has the distinction of being the longest state route in Pennsylvania.