Food has significant societal, historical and religious roles, in addition to nutritional value. It represents cultures and customs, provides opportunities for sharing, giving and social interaction and offers nutrition, pleasure and satisfaction. Technically, all foods are functional, as they fulfill a basic human need and provide nutritive value. However, the term functional food implies an additional physiological benefit beyond meeting basic nutritional needs. Functional food is not only a dietary product providing basic nutritional function of supplying nutrients but it is also known as a health-promoting and/or disease-preventing substance. Functional food has been recognised as a separate category in the food market and it is one of the worlds most intensive areas of food product innovation. This book discusses the sources, health effects and future perspectives of functional foods.