The Clark-Fisher model shows how an economy's sectors change as it develops through different stages. In pre-industrial economies, the primary sector (e.g. mining, agriculture) dominates. During industrialization, the secondary sector (manufacturing) grows to support population and demand. In post-industrial economies, the tertiary sector (services) becomes most important as manufacturing declines. Some developed economies have progressed to a quaternary sector focused on research and IT. Globalization may accelerate these shifts, and different countries may develop through alternative paths.

1. Clark-Fisher Model