Interstate 635 or the Lyndon B. Johnson Freeway (abbreviated I-635 or locally, LBJ) is a 37 miles (60 km) long partial loop around Dallas, Texas (USA) between Interstate 20 in Balch Springs, Texas and State Highway 121 at the north entrance of the Dallas-Fort Worth International Airport in Grapevine, Texas. It intersects Interstate 35E at Exits 27 B-C, but does not connect with Interstate 35W. It is known locally as the Lyndon B. Johnson Freeway, or "LBJ" (named after the president).

Because the portion of I-20 between US 67 to I-635 retains the name of Lyndon B. Johnson Freeway, together with the I-635 freeway, the two highways can be considered a partial (or 3/4) orbital road.

Interstate 635 begins at an intersection with I-20 in southeast Dallas, and travels northward through Balch Springs into Mesquite, where intersects US Route 80 and I-30. The route then turns to the northwest, continuing near the border between Dallas and Garland. 6 miles (9.7 km) later is takes a general westward turn as it intersects U.S. Route 75 at the High Five Interchange. The section from Interstate 35E to U.S. Highway 75 (Central Expressway) is one of the busiest stretches of road in the Dallas-Fort Worth Metroplex, at virtually all hours of the day and night. The route continues west, intersecting the Dallas North Tollway and its original terminus, Interstate 35E in Farmers Branch. The route then continues to the northwest, intersecting the President George Bush Turnpike in Irving before arriving at its final terminus at State Highway 121 at the north entrance to the Dallas-Fort Worth International Airport.

Interstate 635 was originally designated by the Texas Department of Transportation in 1959 as a loop around the eastern side of Dallas, connecting with I-35E to the northwest and southwest sides of the city.

In January 1969, the first section to open to motorists was a 10-mile (16 km) section from US 75 to Barnes Bridge in Mesquite[clarification needed]. In February 1970, the highway from US 75 westward to Interstate 35E northwest of Dallas opened to traffic. The I-635 designation was truncated in 1971 when Interstate 20 was rerouted south of Dallas, taking over 13 miles (21 km) of I-635's former route.

The connecting section of I-20 from the west was not completed until 1978. Initially, the section between I-35E and US 80 in southeast Dallas was concurrent with I-20. When the outlet for I-20 from southeast of Dallas to Terrell was completed, the I-635 designation was removed from I-35E to its intersection with I-20.

An additional westward expansion (to the north entrance of DFW Airport) was designated in 1974 and opened in the 1980s.

The High Five construction project (so called because it is five levels and rises almost 120 feet (40 m) above the lowest level), a rebuild of the interchange of I-635 and US 75, was opened for traffic in February 2006. This interchange carries over 500,000 vehicles per day and was built as the largest interchange in the state of Texas to handle this vehicle load.

A 2.7 billion dollar project was started on May 16, 2011 to widen I-635 and dig subsequent HOT lane tunnels beneath the primary roadway from I-35E to the High Five Interchange, a length of seventeen miles. Construction time is estimated at five years. The project is among several billion dollar plus projects in the planning phase in and around downtown Dallas (along with the rebuild of the I-35E & I-30 "Mixmaster" and the new Trinity Parkway).[citation needed]