ISP, or Internet Service Provider, is a blanket term that covers a wide range of organizations and businesses that offer Internet-related services. The term is used most frequently to refer to companies that provide Internet connectivity to end-user customers, but also covers a broad spectrum of service types that do not relate to providing Internet connectivity.

In a legal sense, even a site like YouTube is considered an ISP, a designation that has significant implications in areas like intellectual property law. Major ISP types include access providers, domain name registrars, web hosts, leased line access and dial-up access, among many others.

Internet Service Providers played a key role in the development of the commercial Internet, which was initially developed as a series of closed networks maintained by government research facilities and select universities that were assisting them. Late in the 1980s, the Web began to move toward commercial applications, with the first private commercial ISPs launching in 1989.

Many major access ISPs are also major telecommunications or cable TV companies, like Comcast, AT&T, Time Warner Cable, CenturyLink, Charter, Verizon, and Cox Communications. Other significant access ISPs have included Optimum, EarthLink, Cable One, Frontier, Suddenlink, NetZero, MSN, Mediacom, Basic ISP,, AOL and Juno.