An Internet service provider (ISP, also called Internet access provider or IAP) is a company which primarily offers their customers access to the Internet using dial-up or other means of data telecommunication.

ISPs may provide Internet e-mail accounts to users which allow them to communicate with one another by sending and receiving electronic messages through their ISPs' servers. ISPs may provide other services such as remotely storing data files on behalf of their customers, as well as other services unique to each particular ISP.

End-User-to-ISP Connection

ISPs employ a range of technologies to enable consumers to connect to their network.

For home users and small businesses, the most popular options include dial-up, DSL (typically Asymmetric Digital Subscriber Line, ADSL), broadband wireless, cable modem, fiber to the premises (FTTH), and Integrated Services Digital Network (ISDN) (typically basic rate interface).

For customers with more demanding requirements, such as medium-to-large businesses, or other ISPs, DSL (often SHDSL or ADSL), Ethernet, Metro Ethernet, Gigabit Ethernet, Frame Relay, ISDN (BRI or PRI), ATM, satellite Internet access and synchronous optical networking (SONET) are more likely to be used.

With the increasing popularity of downloading music and online video and the general demand for faster page loads, higher bandwidth connections are becoming more popular.Fact: date=July 2008

Typical home user connection

• DSL
• Broadband wireless access
• Cable modem
• FTTH
• ISDN

Typical business type connection

• DSL
• SHDSL
• Ethernet technologies

When using a dial-up or ISDN connection method, the ISP cannot determine the caller's physical location to more detail than using the number transmitted using an appropriate form of Caller ID; it is entirely possible to e.g. connect to an ISP located in Mexico from the U.S. Other means of connection such as cable or DSL require a fixed registered connection node, usually associated at the ISP with a physical address.

ISP Interconnection

Just as their customers pay them for Internet access, ISPs themselves pay upstream ISPs for Internet access.

In the simplest case, a single connection is established to an upstream ISP and is used to transmit data to or from areas of the Internet beyond the home network; this mode of interconnection is often cascaded multiple times until reaching a Tier 1 carrier. In reality, the situation is often more complex. ISPs with more than one point of presence (PoP) may have separate connections to an upstream ISP at multiple PoPs, or they may be customers of multiple upstream ISPs and may have connections to each one of them at one or more point of presence.