In England, old ale was strong beer traditionally kept for about a year, gaining sharp, acetic flavours as it did so. The term is now applied to medium-strong (typically above 5%) dark beers, some of which are treated to resemble the traditional old ales. In Australia, the term is used even less discriminately, and is a general name for any dark beer.

The term is sometimes associated with stock ale or, archaically, keeping ale, in which the beer is held at the brewery.

Historically, old ales served as a complement to mild ales, and in pubs of the era typically the landlord would serve the customer a blend of the sharper stock ale with the fruitier, sweeter mild ale to the customer's taste.

Some modern brewers will still make a strong old ale for bottling. Some of these can mature for several years after bottling, and may or may not be bottle-conditioned.

A number of breweries, particularly in Sussex, produce a weaker style of old ale with some resemblance to a mild ale and are typically draught.