In the U.S. state of Idaho, U.S. Route 95 is a north–south highway near the western border of the state, stretching from Oregon to British Columbia for over 538 miles (866 km). It was earlier known in the state as the North and South Highway.

US 95 continues into Idaho from southeastern Oregon as an undivided two-lane highway for the majority of its length. As it is the state's primary north–south highway, Idaho is in the process of widening US 95 to an Interstate-style divided four-lane highway, from the Oregon state line in the southwest to Eastport at the northern border with Canada (Kingsgate, BC).

US 95 departs Malheur County, Oregon, and enters Idaho in the high desert of Owyhee County, about 50 miles (80 km) southwest of Boise. It progresses north-northeast to just west of Marsing, where it meets with the southern terminus of State Highway 55. US 95 then turns briefly west, then north to Homedale, and crosses the Snake River before a junction with concurrent US 20 and US 26 as it passes through Parma. US 95 runs north concurrent with US 20 and US 26 for eight miles (13 km).

As it proceeds north near Idaho's western border, US 95 crosses Interstate 84 (exit 3) and US 30 before proceeding north through Payette and Weiser. It continues on to Midvale, Cambridge, and Council, then climbs into the Payette National Forest, passing the Tamarack sawmill site, and turns east to New Meadows. Here, US 95 joins with Highway 55, the two-lane undivided route that connects to Boise through McCall, Cascade and Horseshoe Bend. The elevation at the junction in New Meadows is 3,865 feet (1,178 m) above sea level.

US 95 continues north through Meadows Valley north of the junction (roadcam), then descends 2,000 feet (610 m) with the Little Salmon River to Riggins, tree-sparse but surrounded by mile-high mountains (vertical drop). Immediately after Riggins, the highway crosses the main Salmon River and enters the Pacific Time Zone. US 95 northbound gradually descends with the widening river until White Bird, where it climbs 2700 vertical feet (820 m) in 7 miles (11 km) to the cut at the top of White Bird Hill, peaking at an elevation of 4,245 feet (1,294 m) (roadcam) with an average gradient of over 7%. The steeper, straighter, and faster multi-lane grade was opened in June 1975, after ten challenging years of construction. The two-lane road of 1921 to the east was first paved in 1938; it left the Salmon River at White Bird Creek following it up through the town of White Bird, and then gradually climbed the grade in twice the distance, with multiple switchback curves. The arcs, if combined, would form 37 full 360° circles, an average of 950° per mile (590° per km). Following the completion of the new steel bridge over White Bird Creek, the new routing opened in June 1975, ending a decade of construction. The new Lewiston grade to the north was finished in just over two years.

North of the summit, US 95 descends in a steep but relatively short descent (roadcam) to the Camas Prairie and Grangeville at 3,390 feet (1,030 m). The highway then travels northwest towards Cottonwood, whose bypass was finished in 1976, then enters the Nez Perce Indian Reservation. New route construction in the early 1990s bypassed the main streets of Ferdinand and Craigmont. The new routing is now above, rather than in, the curvy Lawyers Creek Canyon between the cities, crossing the canyon on an elevated bridge (photo) constructed in 1991. US 95 winds its way westward across the high prairie, near the many timber railroad trestles of the Camas Prairie Railroad, to just east of Winchester. Here, at just under 4,000 feet (1,220 m), the highway turns northward and descends over 3,000 vertical feet (900 m), mostly in the Lapwai Canyon (photos), passing Culdesac, Lapwai, and Spalding at 807 feet (246 m).

Until 1960, US 95 was routed through Winchester and descended Culdesac Hill (46°19′55″N 116°37′59″W / 46.332°N 116.633°W / 46.332; -116.633), considered the worst of the three major grades (White Bird, Lewiston), all of which were extremely twisty. The new route through Lapwai Canyon was built in three years and reduced the distance by over four miles (6 km) and saved 25 minutes of driving time.

After Spalding, it then proceeds towards the bridge over the Clearwater River to join with US 12 and depart the reservation.

After crossing the river, US 95 joins with US 12 for seven miles (11 km) along its north bank, heading westward, adding lanes, and gradually descending toward Lewiston. The highways split at the northeast edge of Lewiston, as US 12 then briefly turns south to re-cross the river into Lewiston, and then heads west again to cross the Snake River into Clarkston, Washington.

US 95 turns northeast, then westward to climb a steep grade, gaining over 1900 vertical feet (580 m) in 5 miles (8 km), ascending to the southern edge of the rolling Palouse region. The multi-lane grade (averaging over 7%) was opened on October 28, 1977, after 27 months of construction and two decades of planning. It replaced the Lewiston Spiral Highway, a narrow and switchback-laden 1917 route to the west with 64 spiral curves and about twice the length; it is visible from a scenic overlook. Similar to the White Bird Hill grade, the descending southbound lanes on the new route have three "run-away truck ramps" to halt any vehicles that experience brake failure.

Just north of the Lewiston grade is a junction with US 195, which proceeds north in Washington to Pullman and Spokane. US 95 continues north in Idaho on the Palouse as a four-lane divided highway (roadcam), completed in October 2007 to Thorn Creek Road (46°37′41″N 116°59′46″W / 46.628°N 116.996°W / 46.628; -116.996), midway between Genesee and Moscow. It then reverts to a two-lane undivided roadway for several miles until Moscow, home of the University of Idaho. Scheduled to be completed first, the divided highway construction between Thorn Creek and Moscow was put on hold, due to new right-of-way and environmental impact concerns. In Moscow, US 95 is diverted a block to either side of Main Street onto multi-lane one-way arterials: northbound on Washington Street, southbound on Jackson Street. The original couplets of 1981 used existing streets and were later modified to eliminate sharp right angle turns which were difficult for large trucks to safely manage. The north end couplets were completed in the early 1990s, the south end in 2000.

North of Moscow, US 95 resumes as an undivided two-lane highway. As it leaves Latah County, it gradually departs the Palouse and enters the lake country region of the north Panhandle. As it enters Benewah County, US 95 enters the Coeur d'Alene Indian Reservation. US 95 intersects State Highway 5 in Plummer. US 95 becomes a four-lane divided highway as it leaves Worley and has an interchange with State Highway 58. This recently completed section bypasses the tribal casino. US 95 continues north as a divided highway until just south of the Spokane River, where US 95 enters Coeur d'Alene.

US 95 becomes an arterial street and crosses over Interstate 90 Business (Northwest Boulevard) at an interchange. US 95 crosses Interstate 90 at exit 12 and becomes a divided highway north to Hayden, then as an undivided highway past State Highway 54 and Farragut State Park. After crossing the Sandpoint Long Bridge, US 95 enters Sandpoint and has a junction with US 2. US 2 and US 95 run concurrent for 35 miles (56 km), until a few miles after Bonners Ferry, where US 2 heads east into Montana and southeast to Libby, while US 95 continues north for 29 miles (47 km) to the Canadian border at Eastport. At the border, US 95 meets BC 95, which continues northeastward in British Columbia to Cranbrook.

US 95 is one of the original routes in the AASHTO's 1926 plan.