Maryland Route 23 is a state highway in the U.S. state of Maryland. The state highway runs 20.58 miles (33.12 km) from U.S. Route 1 in Hickory north and west to the Pennsylvania state line near Norrisville, where the highway continues as Pennsylvania Route 24. MD 23 is an L-shaped highway in northwestern Harford County that consists of two major sections. Between US 1 and MD 165 in Jarrettsville, MD 23 is marked east–west along a two-lane road with partial control of access named East–West Highway. From MD 165 to the state line, the state highway is marked north–south along Norrisville Road, a rural two-lane highway that passes through the villages of Madonna and Shawsville. The two sections of MD 23 are connected by a short concurrency with MD 165.

Pennsylvania Route 24 is a 29-mile-long (47 km) state highway located within central Pennsylvania in the York County area. Its southern terminus is at the Mason–Dixon Line near Stewartstown, where PA 24 continues into Maryland as Maryland Route 23. The northern terminus is at PA 921 in Mount Wolf. The route heads north from the state line through rural areas in southern York County, intersecting PA 851 in Stewartstown and PA 216 in Winterstown. PA 24 continues north to Red Lion, where it crosses PA 74 and intersects the south end of PA 624. The route runs through suburban areas to the east of York, crossing PA 124, PA 462, and U.S. Route 30. PA 24 continues north through rural land and reaches its end in Mount Wolf.