A blended whiskey (or whisky) is the product of blending different types of whiskeys and often also neutral and near-neutral spirits, coloring, and flavorings. It is generally the product of mixing one or more higher quality straight or single malt whiskies with neutral spirits and water. Scotland, Ireland, Canada, and the United States are common countries of origin for blends.
Use of neutral spirits 
Neutral spirits, near-neutral spirits and other 'fillers' are usually much cheaper to produce than straight whiskey or single malt whisky, and are thus used as the primary liquor in blends with those more premium whiskies added for flavouring. Most cocktails and mixed drinks that contain whiskey call for the use of blended whiskey. This is primarily for cost reasons, and secondarily because the complex flavours of higher quality whiskeys would be overshadowed by the mixers.
Scotland and Ireland 
Scottish and Irish blended whiskeys often contain light spirits that are very neutral in flavouring – as the governing regulations in those countries allow whisky distillation processes to reach up to concentrations of 94.8% alcohol by volume (ABV), which is very near the achievable limits of ordinary distillation technology. Scotch and Irish regulations also allow the addition of caramel color, regardless of whether the final product is labelled as blended or not. A mix of single malts only, without other types of whisky such as those made from grains other than malted barley, may be called a blended malt (formerly known as a vatted malt). Under current Scotch whisky regulations, the term vatted is now prohibited for labels, in favor of the term blended malt. In Scotland, when a blended whisky includes an age statement, each individual spirit in the mix must be at least as old as the age listed.
United States 
Blended American whiskey must contain a minimum of 20% straight whiskey, which is made from a distillate not over 160 proof with a mash bill greater than 51% its respective grain and aged for over two years in newly charred barrels. (Corn whiskey has slightly different specifications at over 81% corn mash and aged in used or uncharred barrels, but there are no blended corn whiskeys currently on the market.) Generally, any distilled spirit of 170 proof or higher (without additives) is considered to be essentially neutral alcohol.
Most Canadian whiskeys are blends. Any grain spirit aged for at least three years in Canada may be called Canadian whiskey. Regulations do not specify any distillation limit, although in practice it differs little from the Scottish and Irish limit of 94.8%, as the purity of neutral grain spirit has a practical limit of approximately that value. (A mixture of ethanol and water becomes an azeotrope at 95.6% ABV.) Canadian whiskey may contain both caramel and flavorings, as well as other distilled grain spirits.
Age statements 
Most blended whiskeys do not list an age, although the regulations governing its production in some countries specify a minimum aging requirement. Canadian, Scottish, and Irish whiskey must all be aged at least three years. In the United States, the age statement only refers to the minimum age of the straight whiskey used within the blend (which must comprise at least 20% of the content). As neutral spirits are not considered whiskey, they need not be aged at all in the final product.
- "Standards of Identity for Distilled Spirits, Title 27 Code of Federal Regulations, Pt. 5.22". Retrieved 2008-10-17.
- Lichine, Alexis. Alexis Lichine’s New Encyclopedia of Wines & Spirits (New York: Alfred A. Knopf, 1987), 365.