One classical breakdown of economic activity distinguishes three sectors: In the 20th century, economists began to suggest that traditional tertiary services could be further distinguished from "quaternary" and quinary service sectors. Economic activity in the hypothetical quaternary sector comprises information- and knowledge-based services, while quinary services include industries related to human services and hospitality. Economic theories divide economic sectors further into economic industries.

Historic evolution

An economy may include several sectors that evolved in successive phases: Even in modern times, developing countries tend to rely more on the first two sectors, in contrast to developed countries.

By ownership

An economy can also be divided along different lines: