A service provider (SP) provides organizations with consulting, legal, real estate, communications, storage, processing. Although a service provider can be an organizational sub-unit, it is usually a third party or outsourced supplier, including telecommunications service providers (TSPs), application service providers (ASPs), storage service providers (SSPs), and internet service providers (ISPs). A more traditional term is service bureau (esp. 1960s to 1980s).
IT professionals sometimes differentiate between service providers by categorizing them as type I, II, or III.
The three service types are recognized by the IT industry although specifically defined by ITIL and the U.S. Telecommunications Act of 1996.

Type I: internal service provider
Type II: shared service provider
Type III: external service providerType III SPs provide IT services to external customers and subsequently can be referred to as external service providers (ESPs) which range from a full IT organization/service outsource via managed services or MSPs (managed service providers) to limited product feature delivery via ASPs (application service providers).