1400 Smith Street is a 691 ft (211 m) tall skyscraper located in downtown Houston, Texas, United States. The building has 50 floors and is the 11th tallest building in the city. Designed by architectural firm Lloyd Jones Brewer and Associates, the building was completed in 1983. The 1,200,000-square-foot (110,000 m2) office tower is situated on Houston's six-mile (10 km) pedestrian and retail tunnel system that links many of the city's downtown towers. It was formerly Four Allen Center, a part of the Allen Center complex.

The Houston tunnel system is a network of subterranean, climate-controlled, pedestrian walkways that links 95 full city blocks 20 feet (6 m) below Houston's downtown streets. It is approximately six miles (9.7 km) long. There are similar systems in Chicago, Dallas, Oklahoma City, Montreal, and Toronto. Architectural historian Stephen Fox has stated that the idea for the tunnel system came when the Bank of the Southwest Building was "linked by tunnel to the 1010 Garage and the Mellie Esperson Building" in 1961.