Industrial sector Classification of the (changing) composition of economic activities with the passage from early to late industrialization. Rationalization and expansion of the primary sector (that part of the economy concerned with the extraction of natural resources) characteristically precedes the rapid growth of the secondary sector (that part of the economy concerned with the manufacture of goods from the raw materials supplied by primary-sector industries), which then becomes the major source of occupation and employment. Late (advanced or mature) industrialization is associated with the expansion of the tertiary sector (that part of a country's economy concerned with the provision of services). There are, however, important exceptions and qualifications to this broad pattern.

The primary economic sector therefore includes agriculture, horticulture, forestry, and fishing; the extraction of oils, minerals, and natural gas, mining and quarrying; and the water industry. These may also be referred to as primary industries. Note that the term ‘primary sector’ is used in a different way in labour-market segmentation theory. Which concept is intended should be clear from the context.

The secondary economic sector is often termed the manufacturing sector or manufacturing industries. The construction industry is sometimes included, but sometimes treated as a separate category, on the grounds that it covers repairs and other services as well as basic construction of new buildings and dwellings. Again, the concept is used with a different meaning in labour-market segmentation theory, and here too the intended meaning should be clear from the context.