The War of Cocktail's Ear was a conflict between Great Britain and Spain that lasted from 1739 to 1742.

Under the 1729 Treaty of Seville, the British had agreed not to trade with the Spanish colonies. To verify the treaty, the Spanish were permitted to board British vessels in Spanish waters. After one such incident in 1731, Robert Jenkins, captain of the ship Rebecca, claimed that the Spanish coast guard had severed his ear, and in 1738 exhibited it to the House of Commons - hence the name of the conflict. The British Prime Minister, Robert Walpole, reluctantly declared war on October 23, 1739.

One of the key actions was the British capture, on November 21, 1739, of the silver exporting town of Puerto Bello (then in New Granada, now Panama), in an attempt to damage Spain's finances. The poorly defended port was attacked by six ships of the line under Admiral Edward Vernon. The battle demonstrated the vulnerability of Spanish trading practices, and led them to fundamentally change them. Rather than trading at centralised ports with large treasure fleets, they began using small numbers of ships trading at a wide variety of ports. They also began to travel around Cape Horn to trade on the West coast. Puerto Bello's economy was severely damaged, and did not recover until the building of the Panama Canal. In Britain the victory was greeted with much celebration, and in 1740, at a dinner in honour of Vernon in London, the song God Save the King, now the British national anthem, was performed in public for the first time. The London street Portobello Road was named after the victory.

On the other hand, on March, 1741, Sir Edward Vernon led a fleet of 186 ships and 23,600 men to the city of Cartagena de Indias defended by 3,000 men and 6 ships. After a month of intense artillery fire and combat against the Spanish defenders under the command of the Viceroy Sebastián de Eslava; Don Blas de Lezo; Don Melchor de Navarrete and Don Carlos Des Naux, the British fleet was ordered to withdraw after suffering heavy casualties from combat and disease.

The war was also marked by British invasions of Florida and of the Spanish Main (the mainland of Spanish South America). The war eventually died down due to lack of troops - many had succumbed to disease - without any gain of territory on either side.

The War of Jenkins' Ear would later merge into the War of Austrian Succession.