Highway 4 is a major highway in the Canadian province of Saskatchewan. It runs from U.S. Route 191 at the United States border near Monchy to Highway 224 / Highway 904 in Meadow Lake Provincial Park. Highway 4 is about 652 km (405 mi) long.

U.S. Route 191 is a spur of U.S. Route 91 that has two segments. The southern segment runs for 1,102 miles (1,773 km) from Douglas, Arizona on the Mexican border to the southern part of Yellowstone National Park. The northern segment runs for 442 miles (711 km) from the northern part of Yellowstone National Park to Loring, Montana, at the Canada–US border. Unnumbered roads within Yellowstone National Park connect the two segments. The highway passes through the states of Arizona, Utah, Wyoming, and Montana.