The siege of St. Augustine was a military engagement that took place during June–July 1740. It involved a British attack on the city of St. Augustine in Spanish Florida and was a part of the much larger conflict known as the War of Jenkins' Ear.

Spanish Florida was the first major European land-claim and attempted settlement-area in northern America during the European Age of Discovery. La Florida formed part of the Captaincy General of Cuba, the Viceroyalty of New Spain, and the Spanish Empire during Spanish colonization of the Americas. While its boundaries were never clearly or formally defined, the territory was initially much larger than the present-day state of Florida, extending over much of what is now the southeastern United States, including all of present-day Florida plus portions of Georgia, South Carolina, North Carolina, Alabama, Mississippi, and the Florida Parishes of Louisiana. Spain based its claim to this vast area on several wide-ranging expeditions mounted during the 16th century. A number of missions, settlements, and small forts existed in the 16th and to a lesser extent in the 17th century; they were eventually abandoned due to pressure from the expanding English and French colonial settlements, the collapse of the native populations, and the general difficulty in becoming agriculturally or economically self-sufficient. By the 18th century, Spain's control over La Florida did not extend much beyond a handful of forts near St. Augustine, St. Marks, and Pensacola, all within the boundaries of present-day Florida.