Highway 4 is the longest east–west main vehicle route on Vancouver Island, British Columbia, Canada, with a total length of 162 km (101 mi).

Highway 4 hugs the shore of Cameron Lake for 5 km (3 mi), then winds its way through MacMillan Provincial Park, which includes a tourist attraction known as Cathedral Grove.

After Cameron Lake, Highway 4 climbs for 8 km (5 mi), following the Cameron River, to the Port Alberni Summit—the highest point on the highway (elevation: 411 metres (1,348 ft)), known by locals as "The Hump", at which it crosses from the Regional District of Nanaimo into the Alberni-Clayoquot Regional District—and then descends for 6 km (4 mi) to a spur that travels into the city centre of Port Alberni.

This winding bearing of Highway 4, which features very steep grades, continues for 23 km (14 mi) before reaching the southeast shore of Kennedy Lake.

The 4 and 4A alignments east and north of Coombs, respectively, switched designations when the Parksville to Mud Bay section of the Inland Island Highway was completed in 1996.