Economic activity can be classified into five sectors:
1) The primary sector involves extraction of natural resources and includes activities like agriculture, fishing, mining and forestry. It dominates in underdeveloped countries.
2) The secondary sector transforms raw materials into goods through manufacturing and industry. It contributes moderately to national income in developed countries.
3) The tertiary sector provides services to consumers and businesses. It accounts for most employment in developed countries.
4) The quaternary sector is knowledge-based and includes information technology, research and development, and knowledge services.
5) The quinary sector involves the highest levels of decision making in government, science, and other major institutions.