Mash ingredients, mash bill, mashbill, or grain bill are the materials that brewers use to produce the wort that they then ferment into alcohol. Mashing is the act of creating and extracting fermentable and non-fermentable sugars and flavor components from grain by steeping it in hot water, and then letting it rest at specific temperature ranges to activate naturally occurring enzymes in the grain that convert starches to sugars. The sugars separate from the mash ingredients, and then yeast in the brewing process converts them to alcohol and other fermentation products.

A typical primary mash ingredient is grain that has been malted. Modern-day malt recipes generally consist of a large percentage of a light malt and, optionally, smaller percentages of more flavorful or highly colored types of malt. The former is called "base malt"; the latter is known as "specialty malts".

The grain bill of a beer or whisky may vary widely in the number and proportion of ingredients. For example, in beer-making, a simple pale ale might contain a single malted grain, while a complex porter may contain a dozen or more ingredients. In whisky production, Bourbon uses a mash made primarily from maize (often mixed with rye or wheat and a small amount of malted barley), and single malt Scotch exclusively uses malted barley.