The Battle of the Alamo (February 23 – March 6, 1836) was a pivotal event and military engagement in the Texas Revolution. Following a 13-day siege, Mexican troops under President General Antonio López de Santa Anna reclaimed the Alamo Mission near San Antonio de Béxar (modern-day San Antonio, Texas, United States), killing most of the occupants. Santa Anna's refusal to take prisoners during the battle inspired many Texians and Tejanos to join the Texian Army. Motivated by a desire for revenge, as well as their written desire to preserve a border open to immigration and the importation and practice of slavery, the Texians defeated the Mexican Army at the Battle of San Jacinto, on April 21, 1836, ending the rebellion in favor of the newly formed Republic of Texas.

Several months previously, Texians, who were primarily recent immigrants from the US, had killed or driven out all Mexican troops in Mexican Texas. About 100 Texians were then garrisoned at the Alamo. The Texian force grew slightly with the arrival of reinforcements led by eventual Alamo co-commanders James Bowie and William B. Travis. On February 23, approximately 1,500 Mexicans marched into San Antonio de Béxar as the first step in a campaign to retake Texas. For the next 10 days, the two armies engaged in several skirmishes with minimal casualties. Aware that his garrison could not withstand an attack by such a large force, Travis wrote multiple letters pleading for more men and supplies from Texas and from the United States, but the Texians were reinforced by fewer than a hundred men, because the United States had a treaty with Mexico at the time, and supplying troops and weapons would have been an overt act of war against Mexico.

In the early morning hours of March 6, the Mexican Army advanced on the Alamo. After repelling two attacks, the Texians were unable to fend off a third attack. As Mexican soldiers scaled the walls, most of the Texian fighters withdrew into interior buildings. Those who were unable to reach these points were slain by the Mexican cavalry as they attempted to escape. Between five and seven Texians may have surrendered; if so, they were quickly executed. Several noncombatants were sent to Gonzales to spread word of the Texian defeat. The news sparked both a strong rush to join the Texian army and a panic, known as "The Runaway Scrape", in which the Texian army, most settlers, and the government of the new, self-proclaimed but officially unrecognized Republic of Texas fled eastward toward the U.S. ahead of the advancing Mexican Army.

Within Mexico, the battle has often been overshadowed by events from the Mexican–American War of 1846–1848. In 19th-century Texas, the Alamo complex gradually became known as a battle site rather than a former mission. The Texas Legislature purchased the land and buildings in the early part of the 20th century and designated the Alamo chapel as an official Texas State Shrine. The Alamo has been the subject of numerous non-fictions beginning in 1843. Most Americans, however, are more familiar with the myths and legends spread by many of the movie and television adaptations, including the 1950s Disney miniseries Davy Crockett and John Wayne's 1960 film The Alamo.