HemisFair '68 was the official 1968 World's Fair (or International Exposition) held in San Antonio, Texas, from April 6 through October 6, 1968. Local businessman and civic leader, Jerome K. Harris Sr., coined the name HemisFair and conceived the idea for the fair, hoping it would unite all the cultures that comprise San Antonio and solidify the city's reputation as a cultural and historic destination. With help from commissioner Henry B. Gonzales and other San Antonio leaders, the fair materialized and helped transform the city from a cowtown to one of the largest cities in the country. The theme of the fair was "The Confluence of Civilizations in the Americas", celebrating the many nations which settled the region. The fair was held in 1968 to coincide with the 250th anniversary of the founding of San Antonio in 1718. More than thirty nations and fifteen corporations hosted pavilions at the fair.

The Bureau International des Expositions (BIE) which oversees World's Fairs and Expositions, awarded HemisFair '68 with official Fair status on November 17, 1965.

The theme character of the fair was a dragon named Luther created by Sid and Marty Krofft, who was later renamed and starred in the Kroffts' Saturday morning television show H.R. Pufnstuf. The main premise of the show was taken from their production for the Coca-Cola pavilion at the fair.

The venture, which had an announced cost of $156 million, was financed by a combination of public and private funds. Public funding included $12.2 million from the U.S. Housing and Home Finance Agency for acquiring and clearing the site, $11 million in publicly approved city bonds for construction of the convention center and arena, $5.5 million in general revenues from the City of San Antonio for construction of the Tower of the Americas, $10 million from the State of Texas primarily for the construction of the Texas State Pavilion, and $7.5 million from the United States Congress for the construction of the United States pavilion.

Although HemisFair '68 attracted 6.3 million visitors and brought international attention to San Antonio and Texas, attendance never matched predictions, and the fair lost $7.5 million.

The fair was built on a 96.2-acre (389,000 m²) site on the southeastern edge of Downtown San Antonio. The site was acquired mainly through eminent domain. Many structures in what was considered a blighted area were demolished and moved to make room for the fair. The project was partially developed with federal urban renewal funds. The San Antonio Conservation Society recommended that 129 structures on the site be preserved; however, on August 9, 1966, an agreement was made to save only 20 existing structures that would be incorporated into the fair site. Overall, only 24 structures were saved.

In addition, as a part of the overall HemisFair project, the city extended its River Walk (Paseo del Rio) one-quarter of a mile into the site in order to link the River Walk and the HemisFair grounds in 1968. In 2001, the River Walk was extended again under the new Convention Center Expansion and is now connected to a small lagoon inside HemisFair Park.

HemisFair began on April 6, 1968, with the gates opening at 9:00am and official ceremonies beginning at 10:00 am in the new Convention Center Arena. However, with the opening just two days after the assassination of Martin Luther King Jr., VIPs in attendance – including U.S. First Lady Lady Bird Johnson and Texas Governor John Connally, both of whom received death threats – were escorted around the site under heavy security.