In a general sense, an ingredient is a substance which forms part of a mixture. In cooking, recipes specify which ingredients are used to prepare a dish, and the term may also refer to a specific food item in relation to its use in different recipes. Many commercial products contain secret ingredients purported to make them better than competing products. In the pharmaceutical industry, an active ingredient is the ingredient in a formulation which invokes biological activity.

National laws usually require prepared food products to display a list of ingredients and specifically require that certain additives be listed. In the European Union, food labeling regulations also mandate that allergens such as nuts, milk, and gluten be clearly emphasized within the ingredient list to protect consumers.