Inland desert route, commonly known as US 395, but also known as the Three Flags Highway is a U.S. numbered highway in the western United States that traversed the eastern area of Washington, Oregon and California as well as a small section of the extreme western portion of Nevada.

The current southern terminus is in the Mojave Desert near Hesperia at IH 15. South of this terminus, US 395 has been replaced by IH 15, IH 215, and California State Route 163, which was the US 395 route from Hesperia to San Diego through Riverside and San Bernardino. The Old Highway 395 can be seen along or near I-15 in many locations before it branches off at Hesperia to head north.

Before 1964, the route extended south into San Diego to the corner of 11th and Ash in downtown San Diego. This part of the highway is now the alignments of Interstate 15 from Hesperia to Devore and Interstate 215 from Devore, through San Bernardino, Grand Terrace, Riverside, Moreno Valley, Perris, and Menifee to Murrieta where it meets Interstate 15 again.

From Murrieta the old route follows Interstate 15 again to east of Fallbrook where the original US 395 still exists as a frontage road. The Old US 395 can be followed from north of State Route 76 through Escondido where it meets Interstate 15 again. Finally, State Route 163, the old routing of US 395, splits off Interstate 15 at the south end of Miramar and follows the Cabrillo Freeway into downtown San Diego.

The northern terminus is at the Canada–US border near Laurier, where the road becomes Highway 395 upon entering the US from British Columbia, Canada. From the Canadian border, the highway moves south and traverses primarily desert areas of the several northernmost states through the Basin and Range region and then upon arriving in Nevada and Southern California, enters into the Pacific Coastal region. The southern terminus of the route is in the Mojave Desert at Interstate 15 near Hesperia.