State Highway 99, also known as the Grand Parkway, is a Texas highway, which opened its first section in 1994. When State Highway 99 is complete, it will be the longest beltway in the US, and the third loop within the Houston–Sugar Land–Baytown metropolitan area, with Interstate 610 being the inner loop, and Beltway 8 (Sam Houston Tollway) being the middle loop. The proposed 170-mile (270 km) loop has been divided into 11 separate segments for construction and funding purposes. Only two of the 11 segments are complete. As of December 25, 2011, all segments except A have been fully funded.

In 1926, SH 99 was a minimal highway from Alpine to San Angelo. By 1936, this route was transferred to SH 10. In 1960, a new route was made for SH 99, going from Denton to the Oklahoma line, replacing the old routing of SH 10. SH 10 then was changed to SH 99 to match OK 99 at its border. In 1968, this route became US 377.

Segment D, the first section opened, runs from just north of Interstate 10, west of Houston, south to US 59 in Sugar Land where it terminates and intersects with FM 2759. The portion of this segment south of the interchange with the Westpark Tollway is currently a four-lane divided highway, which will become feeder roads once the main lanes are constructed. The section north of the Westpark Tollway intersection is currently a four-lane controlled-access freeway.

The 18-month-long construction of two ramps connecting westbound I-10 to southbound SH-99 and northbound SH-99 to eastbound I-10 was completed in 2011. The occasional traffic jams at this intersection prompted the sped up construction of the ramps before the through lanes of SH-99 were built through the I-10 interchange. Two more ramps connecting southbound SH-99 to eastbound I-10 and westbound I-10 to northbound SH-99 are planned as part of the construction of Segment E.

Between the Westpark Tollway and US 59, Fort Bend County is constructing toll overpasses at nine locations along Highway 99. Motorists would be charged around 30¢ to use each overpass, or could bypass the toll by using the current roadway through the signalized intersections.

Segment I-2, which opened on March 25, 2008 after five years of construction, runs from Interstate 10 east of Houston south to Business State Highway 146 in Baytown. (The former Spur 55, which ran from FM 1405 to Business 146, was renumbered SH 99 and connects with the newly constructed portion of Segment I-2 at FM 1405.)

TxDOT began collecting tolls on this segment on November 1, 2011. Motorists are able to pay tolls using TxTag, EZ TAG or TollTag transponders. No cash or mail payments are available on this segment. Tag reader gantries have been installed on the mainline just south of FM 565, and on the northbound entrance and southbound exit ramps at FM 565. Tolls will be $1 for two-axle vehicles.

September 2011 construction finally began on Segment E connecting I-10 Katy Freeway in the South to US 290 with a completion set for December 2013. On June 3, 2008 the Harris County Commissioners Court voted to fast track the construction of Segment E with construction to begin in 2009 and then came the addition of $150 million in Stimulus money yet still the project stalled. As with many Stimulus projects it turned out not to be "shovel ready" enough and the $150 million was sent back to TXDOT for use elsewhere. In 2011 the Wetlands permit from the Army Corp of Engineers was finally acquired. In addition, Harris County relinquishing its rights to TXDOT who will construct a Public Private Cooperative toll road. At its April 28, 2011 meeting TXDOT allocated $350 million and the construction permits were let in July 2011. On July 28, 2011 TXDOT reported that three out of four contracts for Segment E were awarded and that construction will start by early September 2011.

The multi year reconstruction of I-10 was completed in 2008 while US 290 reconstruction is not due to even start till 2011. " The 22-mile (35 km) long section of I-10 from the suburb town of Katy to just inside the I-610 loop has expanded it to handle the rapidly expanding western suburbs of Houston not just adding lanes, but also an expanded HOV with two lanes in both directions where there was one lane reversed back and forth with rush hour and a toll lane for commuters willing to pay congestion prices for the quicker ride. The idea put forth is that Segment E is Toll viable from the start meaning it would pay for itself with tolls collected because of the need to relieve traffic on US 290 along with the continued expansion of the western suburbs. After US 290 construction is completed and less traffic is diverting down the E Segment of the Grand Parkway the reasoning is that the inevitable population explosion going on in the area would not just replace the lost traffic from the US 290 completion, but increase its use.

Segment F-1 connects US 290 to Texas State Highway 249. Construction is slated to begin January 2013 completion date in 2015.

Segment F-2 connects Texas State Highway 249 with I-45. Construction is scheduled to start January 2013 completion in 2015.

Segment G connects I-45 with 59 North. Construction is scheduled to start January 2013 completion in 2015

The next section that will be constructed is Section E, most likely followed by either Section F-1, F-2, or G. All of these sections are located northwest and north of Houston. Section E will run from the northern terminus of Section D north to US 290. Section F-1 will start at the end of Section E and end at the intersection with State Highway 249. Section F-2 begins here and terminates at Interstate 45. Section G starts at the end of Section F-2 and travels to US 59.

Future sections of the Grand Parkway will most likely be built as tollways in conjunction with the Harris County Toll Road Authority to speed up the loop's completion. Western sections of the Grand Parkway have been mentioned as possible bypass routes for the Houston section of the proposed Interstate 69 extension to the United States–Mexico border.

On August 16, 2010, the Grand Parkway Association listed the estimated completion of each section. In order of completion:

On June 16, 2011, several changes were made to the time table. The majority of the changes were segments being delayed.

On December 12, 2011, several changes were made to the time table. All of the changes were segments being delayed.

Current residents who live along the Grand Parkway in Harris and Fort Bend counties (namely in the Cinco Ranch/Falcon Point areas within segment D) have noticed increased noise due to expansion of the highway, which includes construction of new overpasses as well as increased growth in the surrounding area. Sound barriers have not been constructed based on a 20+ year environmental study. Resident petitions and protests for a new sound barrier study have not been addressed and Texas DOT claims "This section of the Grand Parkway does not qualify for that." Further expansion in this area is planned to start in 2010 with two tollway lanes added in each direction.

Some groups in some neighborhoods are opposing the idea of the Grand Parkway going through their neighborhoods. For instance, a group called "United to Save Our Spring" is trying to stop the Parkway from going through a neighborhood off FM 2920. Residents in other unincorporated areas such as The Woodlands have not shown the same opposition and support the construction of the Grand Parkway, namely segments E, F-1, F-2, and G, as this would give residents living in the outer suburbs a toll road option to drive to San Antonio, Austin, northeast Texas, or Louisiana without having to drive through the city of Houston.

Some residents in Brazoria County, along segment B, have voiced opposition to several of the proposed alignments. However, TxDOT has recently proposed a fifth alternative alignment to the north of Alvin. This alternative is acceptable to the opposition group Citizens Against the Grand Parkway and is likely to encounter much less opposition from the community.

The controversial segment A, which would stretch from Texas State Highway 146 to Interstate 45 southeast of Houston through a very developed area, has not been fully designed yet. Texas Highway 146 is a possible route of the highway during segment A, but TXDOT has released plans for the highway to intersect I-45 from the west at its intersection with FM-646. This intersection has many businesses around it and could not support a major highway running through it. If the highway continued south on Highway 146 to its intersection with FM 646 (Supposing the highway was built along the route of FM-646), it would eventually have to pass through the town of Kemah, which could not support a large highway unless many businesses were destroyed. A merger with I-45 along the route is much more likely and would cause less public outrage.