The International Standard Industrial Classification of All Economic Activities (ISIC) is a United Nations industry classification system. Wide use has been made of ISIC in classifying data according to kind of economic activity in the fields of employment and health data. It is maintained by the United Nations Statistics Division. ISIC classifies entities by activity. The most detailed categories are defined by combinations of activities described in statistical units, considering the relative importance of the activities included in these classes. ISIC Rev.4 continues to use criteria such as input, output and use of the products produced, but places additional emphasis on production processes.