Baking powder is a leavening agent commonly used in baking to help dough rise. It contains a combination of an acid, usually cream of tartar, and a base, typically baking soda. When mixed with liquid and exposed to heat, it produces carbon dioxide gas, which creates bubbles in the batter or dough, resulting in a light and fluffy texture. There are two main types of baking powder: single-acting and double-acting. Single-acting baking powder releases gas as soon as it is mixed with liquid, while double-acting baking powder releases gas in two stages—once when mixed and again when heated. This makes double-acting baking powder more versatile for various recipes.