Definition and range of functional food will be discussed. The initiation, development and future trend of functional food industry will be introduced .The terms, systems of health food certification and related regulation of health food of various countries will be included and compared. The principle or active components and their functionalities on human body will be interpreted. Toxicology concerns about major compounds in functional products will be included. Nutritional point of views will be applied to explain the role and bioactivities of functional foods.