India Pale Ale (IPA, a variation of which is known as Imperial Pale Ale) is a distinct style of beer and is characterized as a sparkling pale ale with a high level of alcohol (modern day versions are usually greater than 6% APV by volume in the US, although below 5% APV in England the home of IPA, though the original versions were considerably higher then 6%) and hops, thus having an increased bitterness (in modern times typically 35–48 on the IBU scale, though originally probably more than 60 IBU).

The creation of India Pale Ale during the early 1700s was the result of tremendous efforts by British brewers to overcome a difficult problem: during the 1700s beer did not keep well on long ocean voyages, especially into hot climates. These hot environments resulted in the arrival of flat, sour beer. Before refrigeration and pasteurization, the brewer's only weapons against spoilage were alcohol and hops. Alcohol provided an unfriendly environment for microbes and the hops prevented the growth of the bacteria which cause sourness. Therefore high alcohol content and high hopping rates could protect beer from the souring associated with long storage times.

The IPA style is now less common in the United Kingdom; many beers called IPA in the UK are indistinguishable from ordinary session bitters.

In the USA the style has been enthusiastically reproduced in recent years by microbrewers. The original highly hopped and long aged (one full year in wood before bottling) Ballantine IPA has not been brewed for more than 20 years; however at least in part because of that particular brand's legendary status in American brewing, the IPA style has become very popular with American microbreweries, where it has evolved into a distinct variant sometimes called American India Pale Ale. Although some are made to traditional recipes, American IPAs are generally brewed with citric American hop varieties such as Cascade, Chinook, Centennial, and Columbus. American brewers have also altered the style to increase the bitterness of the beer to well over 100 IBUs and the alcohol levels up to 10 or even more than 20 % alcohol by volume.