U.S. Route 70 is an east–west United States highway that runs for 2,385 miles (3,838 km) from eastern North Carolina to east-central Arizona. As can be derived from its number, it is a major east–west highway of the Southern and Southwestern United States. It formerly ran from coast to coast, with the current Eastern terminus near the Atlantic Ocean in North Carolina, and the former Western terminus near the Pacific Ocean in California. Before the completion of the Interstate system, U.S. Highway 70 was sometimes referred to as the "Broadway of America", due to its status as one of the main east–west thoroughfares in the nation.

U.S. 70 begins in Globe at a junction with U.S. Route 60, concurrent with State Route 77. SR 77 splits off east of town. U.S. 70 then enters the San Carlos Apache Indian Reservation and runs southeast for 17 miles (27 km) to Peridot, where it crosses Indian Route 9. It has no other highway junctions until Safford, where it begins a ten-mile (16 km) overlap with U.S. 191. U.S. 70 then runs an additional 37 mi (60 km). (59 km) before crossing into New Mexico east of Franklin.

After entering the state of New Mexico, U.S. 70 heads southeast. Five miles (8 km) after crossing the state line, it serves as the southern terminus for New Mexico State Road 92. U.S. 70 does not have another highway junction for 21 mi (34 km), where it meets State Roads 464 and 90 three miles (5 km) north of Lordsburg. At Lordsburg, U.S. 70 joins with Interstate 10 eastbound, splitting off in Las Cruces, and becoming Picacho Avenue in Las Cruces. When Picacho Avenue meets Main Street, US 70 follows Main Street northbound. U.S. 70 then crosses Interstate 25, and has been upgraded at this point to a controlled access highway until entering the foothills of the Organ Mountains.

As a divided highway, U.S. 70 then crosses the Organ Mountains via San Augustin Pass, descends to the valley floor of the Tularosa Basin, and next crosses the White Sands Missile Range. Overhead missile tests can close the highway for a few hours; this generally happens once or twice a week, and typically only for an hour at a time. The road then passes the entrance to the White Sands National Monument, and shortly after that passes the southern end of Holloman Air Force Base. It then turns northbound, and picks up a concurrency with U.S. 54 upon entering Alamogordo. On the north end of Alamogordo, US54/US70 intersects the beginning of U.S. Route 82 near La Luz. The concurrency with US 54 lasts until Tularosa, and the highway remains divided until US 70 and US 54 diverge. After splitting off to the northeast, U.S. 70 begins an ascent into the Sacramento Mountains and enters the Lincoln National Forest. The road then runs across the Mescalero Apache Indian Reservation and near the resort town of Ruidoso. In Hondo, it begins another concurrency, this time with U.S. 380. U.S. 70 then bypasses Roswell to the northwest, together with U.S. 285. U.S. 70 then heads off to the northeast, running through Portales and Clovis before entering Texas at Texico.

US 70 is the only non-interstate in New Mexico to receive a speed limit of 75 miles per hour.

U.S. 70 enters Texas joined with U.S. 60 and U.S. 84. U.S. 60 splits off to the northeast in Farwell, Texas, just over the state line. U.S. 70/84 then angle southeast to Muleshoe, where the two routes split. U.S. 70 heads due east, meeting U.S. 385 at Springlake, and having an interchange with Interstate 27 in Plainview. U.S. 70 then arcs toward the south to begin a concurrency with US 62 in Floydada. The two routes head east to Paducah, Texas, where US 62 splits off to the north to join with U.S. 83. U.S. 70 then proceeds to Vernon, where it overlaps U.S. 287 and U.S. 183 (and has a junction with U.S. 283). Near Oklaunion, Texas, U.S. 70/183 split off to the north to cross the Red River into Oklahoma. The route through Texas was cosigned with Texas State Highway 28 before 1939. SH 28 was designated in 1919 as a route from Muleshoe to Olney with a spur, SH 28A, from SH 28 at Crowell east to the Oklahoma border. In 1922, the route split in Benjamin, going south to Sagerton and east to Olney. In 1926, The portion from Crowell to Sagerton became SH 51, while the portion from Benjamin to Olney became SH 24. SH 28 was instead rerouted over SH 28A to end at the Oklahoma border. By 1939, the route was cancelled due to US 70.

U.S. 183 splits away from U.S. 70 three miles (4.8 km) north of the state line, in the town of Davidson. It then has an interchange (Exit 5) with Interstate 44, serving as the southern terminus of the H.E. Bailey Turnpike, one mile (1.6 km) west of the town of Randlett. U.S. 70 then passes south of Waurika. U.S. 70 then becomes a four-lane divided highway near Wilson and runs through Lone Grove before entering the city of Ardmore, where it briefly heads south on Interstate 35, bypassing the central business district. US-70 serves as the southern terminus of U.S. 177 in Madill. U.S .70 then heads to Durant, where it has an interchange with the U.S. 69/75 freeway.

East of Soper, U.S.70 joins with U.S.271. The two routes then approach Hugo, where they serve as the southern terminus of the Indian Nation Turnpike. U.S. 271 also splits off at this interchange, continuing the freeway southbound from the turnpike. U.S. 70 then heads through downtown Hugo. It then bypasses Idabel to the north (with Bypass U.S. 70 providing a western and southern bypass). It then meets U.S. 259 and State Highway 3 northeast of town and overlaps them into Broken Bow, forming a wrong-way concurrency with SH-3. U.S. 70 then splits off to the east in Broken Bow before leaving the state.

U.S. 70 enters Arkansas eight miles (13 km) west of De Queen, bypassing the town to the north. Northeast of the city, it meets U.S. 71 and overlaps with it for 8 mi (13 km). It then heads northwest to Dierks, where it begins a concurrency with U.S. 278. U.S. 70 then heads east-northeast to Hot Springs, which it bypasses to the south on a freeway alignment shared with U.S. 270. U.S. 70 then heads east to join with Interstate 30 at Exit 111 south of Benton. The two highways run concurrently to the state capital, Little Rock, where U.S. 70B splits off from I-30 and U.S. 70 at Exit 132, and runs through downtown Little Rock, having an interchange with Interstate 630 before crossing the Arkansas River into North Little Rock. U.S. 70 remains with I-30 through Little Rock, crossing the Arkansas River into North Little Rock. It then splits off from I-30, and is rejoined by U.S. 70B at Exit 141B, and serves as the northern terminus of U.S. Route 165. U.S. 70 then crosses Interstate 440 and leaves the Little Rock area, paralleled by Interstate 40.

U.S. 70 continues its alignment near I-40 throughout eastern Arkansas, generally about two or three miles (5 km) apart. I-40 bypasses Forrest City to the north, while U.S. 70 serves the city center. The two routes remain close through West Memphis, Arkansas, where U.S. 70 runs along Broadway Blvd. Finally, U.S. 70 joins with Interstate 55 to cross the Mississippi River into Tennessee.

US 70 enters Tennessee, as well as the city of Memphis, concurrent with Interstate 55, US 61, US 64, and US 79. At exit 12, the northernmost exit on I-55 in the state, I-55 turns south; however, the four US routes continue east onto the at-grade Crump Boulevard. US 61 splits from the concurrency soon afterward, heading south along 3rd Street to exit the city. US 64, 70 and 79, however, remain overlapped through downtown Memphis, following Danny Thomas Boulevard north to Union Avenue, Union east to East Parkway (briefly overlapping with U.S. Route 51 along the western portion of Union), then East Parkway north to Summer Avenue, where the triple concurrency turns east. Near the city line, US 64/70/79 interchanges with Interstate 40 at exit 12A.

Past the Memphis city limits in the suburb of Bartlett, U.S. 64 separates from U.S. 70/79, taking a more southerly routing through the state. U.S. 70 and US 79, meanwhile, head to the northeast, paralleling I-40 to Brownsville. East the of city, U.S. 79 breaks from U.S. 70, following U.S. 70 Alternate out of the city to the northeast. U.S. 70, now concurrent with only its unsigned designation of State Route 1, heads east, interchanging with I-40 at exit 66 before entering Jackson. The route continues northeast from the city, meeting I-40 once more at exit 87 just outside the city limits. At Huntingdon, U.S. 70 Alternate rejoins US 70 as the main route turns to the east toward New Johnsonville, where it crosses the Tennessee River.

From the river, U.S. 70 continues eastward through Waverly and Dickson to the Nashville area. Southwest of the city near Pegram, U.S. Route 70S splits off from U.S. 70; however, U.S. 70 now continues to be signed as U.S. 70 instead of U.S. 70N, as it was formerly. U.S. 70 follows I-40 into Nashville, meeting the concurrent I-40/I-65 immediately west of the city center. The route turns south, acting as collector/distributor roads for I-40/I-65 for two blocks before joining U.S. 431 and U.S. 70S on a brief overlap. At an intersection with the concurrent U.S. 31/U.S. 41, U.S. 431 and U.S. 70S split from U.S. 70. U.S/ 70 progresses eastward, roughly paralleling the Cumberland River to an interchange with State Route 155 east of downtown. U.S. 70, now paired with State Route 24, heads east out of Nashville to Lebanon, where U.S. Route 70N breaks from the main US 70. US 70 heads southeast, passing through Smithville before rejoining U.S. 70S in Sparta and U.S. 70N to the east in Crossville.

From Crossville eastward to the North Carolina state line, U.S. 70 closely parallels I-40, passing through the Roane County cities of Rockwood and Kingston. At Dixie Lee Junction in eastern Loudon County U.S. 70 (the Lee Highway) intersects U.S. 11 (also known as the Dixie Highway) and the two highways are concurrent from the junction intersection eastward through Farragut and into Knoxville. In Farragut and west of downtown Knoxville U.S. 70 carries the name Kingston Pike. On the east side of Knoxville it becomes concurrent with U.S. 25W and U.S. 11E and carries the name Asheville Highway from Knoxville to the community of Trentville in eastern Knox County. At Trentville, US 11E separates from the concurrency. U.S. 25W remains overlapped with U.S. 70 to Newport, where U.S. 70 is joined by U.S. 25E, which becomes US 25. U.S. 25 and U.S. 70 remain concurrent into North Carolina.

US 70 enters North Carolina as a two-lane road in concurrency with US 25. Going southeast, it widens to four-lane near Marshall, merging farther down with I-26/US 19/US 23 going into Asheville. In the downtown area, it breaks from the freeway onto city streets and through Beaucatcher Tunnel as it goes east; paralleling north of I-40, going through the cities Marion, Morganton, Hickory, Conover and Statesville. From there, it goes southeast to Salisbury, where it starts to parallel I-85 north through Lexington, Thomasville, High Point and Greensboro, in concurrency with I-85 Bus/US 29.

After passing through Greensboro, it again parallels north of I-40/I-85 as a four-lane expressway through the cities of Burlington, Mebane and Hillsborough. It then goes southeast through the downtown areas of both Durham and Raleigh.

After a brief overlap with I-40 near Garner, it continues in a southeasterly direction, as it goes through or bypass the cities of Clayton, Smithfield, Selma, Goldsboro and Kinston. Near and through New Bern, US 70 briefly becomes a freeway but returns to expressway grade as it goes through Havelock. After passing through Morehead City and Beaufort, it drops back to a two-lane rural road as it travels close along the Core Sound. After passing the southern terminus of NC 12 (which connects to the Outer Banks), near Sealevel, US 70 ends its seven state tour in the community of Atlantic.

Most or all of the present route designated as U.S. Highway 70 was earlier known as Lee Highway. During the earliest days of the automobile, and earlier, American highways were disorganized affairs of widely varying quality. Highways were known by a bewildering variety of names which typically changed at each town. And they were only named, not numbered.

During the 1920s the first national highway was conceived: the Lincoln Highway, named in honor of Abraham Lincoln, stretching across the northern United States from coast to coast. A companion effort was launched to create a transcontinental highway stretching across the southern half of the country, this one named in honor of the greatest general of the Confederate States of America, Robert E. Lee. The two highways were a revolution of sorts, in that a driver could follow a single road from coast to coast bearing the same designation. Much of today's U.S. 70 was earlier the Lee Highway, although that appellation was later dropped.

Originally U.S. Highway 70 reached downtown Los Angeles even though it was concurrent with U.S Route 99 and/or U.S. Highway 60 throughout its course west of Globe, Arizona. Beginning in 1964 it was decommissioned in favor of Interstate 10 or US 60.

Bruce Springsteen's 1975 song, "Thunder Road" immortalizes the 1958 Robert Mitchum film, Thunder Road about a family of anarchistic moonshiners who engage in run-ins with the police. The Mitchum film is based on a real life incident in which a moonshiner perishes on the road while on the run from the police.

US 70 has two additional branches in Tennessee, US 70N and US 70S. This split is unique, in that it is the only existing instance of a N/S split of a U.S. highway. Further, US 70 does not "disappear" at these splits; thus, these two highways serve as additional branches of the main route. US 70N begins in Lebanon, Tennessee, just east of Nashville, and ends in Crossville, TN; US 70S begins in the Bellevue neighborhood of southwest Nashville, and ends in Sparta, TN (a few miles west of Crossville). Historically, both split routes began in Pegram and ended in Crossville. The original designation for U.S. 70 between Lebanon and Sparta was state highway 26.

There is a US 70A in Conover, NC and Wilson, OK. Additionally, there is an Alternate US 70 between Brownsville, TN, and Huntingdon, Tenn. Signage along this route, and on most maps, show it as US 70A. Another US 70A, approximately 9 miles (14 km) long, runs from Selma NC to near Princeton, NC. Its western terminus in Selma lies on US 70 in between the endpoints of the US 70 Business Route through Smithfield, NC.