An Internet Service Provider is a company that provides Internet access. Customers can be businesses, individuals and organizations. Two common types of Internet access are dial-up shell accounts and SLIP/PPP accounts.

In a shell account, the user connects to a host computer at the ISP and can then access the Internet through the host computer. All necessary software is on the host machine, not the user's machine. In a SLIP/PPP account, the user has all necessary software installed on his or her computer and connects directly to the Internet through the ISP. Additional services that can be offered by an ISP include web hosting, domain name service and proprietary online services.