The tertiary sector of the economy, generally known as the service sector, is the third of the three economic sectors in the three-sector model (also known as the economic cycle). The others are the primary sector (raw materials) and the secondary sector (manufacturing).

The tertiary sector consists of the provision of services instead of end products. Services (also known as "intangible goods") include attention, advice, access, experience and affective labour.

The tertiary sector involves the provision of services to other businesses as well as to final consumers. Services may involve the transport, distribution and sale of goods from a producer to a consumer, as may happen in wholesaling and retailing, pest control or financial services. The goods may be transformed in the process of providing the service, as happens in the restaurant industry. However, the focus is on people by interacting with them and serving the customers rather than transforming the physical goods. The production of information has been long regarded as a service, but some economists now attribute it to a fourth sector, called the quaternary sector.