The Internet is a global system of interconnected computer networks. These networks exchange data using a shared set of communication rules, the TCP/IP protocol suite. It is a decentralized "network of networks." Thousands of independently operated networks run by universities, companies, governments and internet service providers agree to carry one another's traffic, and no single authority controls the whole system. The Internet carries services such as the World Wide Web, email, file transfer, streaming media and voice and video calls. It has become basic infrastructure for communication, trade, education and science. According to the International Telecommunication Union (ITU), about 6 billion people, roughly 74 percent of the world's population, were using the Internet in 2025.
History
Origins in packet switching
The Internet grew out of research on packet switching in the 1960s. In this method, data is broken into small blocks called packets. Each packet is routed independently across a network and the packets are put back together at the destination. Packet switching made better use of communication lines than the dedicated circuits used in telephony. In 1969 the U.S. Department of Defense's Advanced Research Projects Agency (ARPA) began operating the ARPANET. It started with four nodes and was one of the first wide-area packet-switched networks. Other packet networks appeared around the same time, including the French CYCLADES project and the NPL network in the United Kingdom.
TCP/IP and internetworking
Separate networks used incompatible technologies, so researchers looked for a way to connect them. In the 1970s Vint Cerf and Robert Kahn designed the Transmission Control Program. It drew on ideas from CYCLADES, including simple host-to-host transmission of datagrams. The program was later split into two protocols. TCP handles reliable delivery and error checking, and IP (the Internet Protocol) handles addressing and routing across networks. In November 1977 a test sent data across three different networks: ARPANET, a packet radio network and a satellite network. The U.S. Department of Defense later adopted TCP/IP as a standard. On 1 January 1983, a date known as "flag day," the ARPANET replaced its older Network Control Program with TCP/IP. Many accounts treat this switch as the start of the modern Internet, though some historians argue that internetworking existed before it.
Expansion and commercialization
In the 1980s the U.S. National Science Foundation built NSFNET, a high-speed backbone linking academic networks. Over time it took the place of ARPANET, which was shut down in 1990. The Domain Name System (DNS), introduced in the mid-1980s, translates human-readable names into numeric IP addresses. Restrictions on commercial traffic were gradually lifted, and NSFNET was retired in 1995. After that, commercial providers ran the backbone.
The World Wide Web
The Internet and the World Wide Web are often confused. The Web is one application that runs on top of the Internet. In March 1989, while working at CERN, Tim Berners-Lee proposed a distributed information system for physicists. By the end of 1990 he had developed the main parts of the Web: hypertext documents written in HTML, the HTTP protocol for transferring them, and URLs for locating them. He had also built the first web server and browser. On 30 April 1993 CERN released the Web software royalty-free. Graphical browsers such as Mosaic, released the same year, helped bring the Internet to the general public. The Web spread quickly in the following years.
Technical architecture
The Internet's design is usually described in layers. The physical and link layers move bits over copper cable, optical fiber, radio and satellite links. The internet layer, IP, gives each device an address and sends packets between networks. Routers forward each packet based on its destination address. The transport layer, mainly TCP and UDP, manages communication between programs on the two end devices. The application layer includes protocols such as HTTP, SMTP for email, and DNS.
A key design idea is the "end-to-end principle." The core network stays fairly simple and mostly just forwards packets, while most of the complex work happens at the end devices. This lets new applications be built without changing the network itself. The original addressing scheme, IPv4, offers about 4.3 billion addresses, which proved too few. Its successor, IPv6, uses 128-bit addresses and is being deployed gradually. Large networks exchange routing information through the Border Gateway Protocol (BGP). They connect to one another at internet exchange points and through long-distance links, including submarine cables. Most of the hardware relies on advances in semiconductors.
Governance
No single organization runs the Internet. Technical standards are developed mainly by the Internet Engineering Task Force (IETF). It publishes specifications called Requests for Comments (RFCs). Web standards are developed by the World Wide Web Consortium (W3C), founded in 1994. ICANN coordinates the global systems of domain names and IP addresses, and regional internet registries allocate address blocks. National governments regulate access, content and telecommunications within their borders. Policy debates cover net neutrality, privacy, censorship and jurisdiction. This model, in which governments, companies, technical bodies and civil society all take part, is often called "multistakeholder" governance.
Applications and social impact
The Internet has changed how information is published and found. Search engines, social media and online reference works such as Wikipedia became possible because of it. Large-scale crowdsourcing and collaborative open-source software development depend on it too. Its arrival is often compared to that of printing in its effects on how knowledge spreads. E-commerce, online banking, remote work and distance learning all rely on it. Cloud computing has moved data storage and processing into large data centers that users reach over the network. The huge amount of text and images available online also provided the training data for modern machine learning systems, including large language models.
Mobile access now makes up most of global use. Smartphones are many people's main or only way of getting online. ITU estimated that in 2025, 5G networks covered about 55 percent of the world's population.
Challenges
Digital divide. Access is uneven. In 2025 about 2.2 billion people were still offline, and 96 percent of them lived in low- and middle-income countries. Internet use was 94 percent in high-income countries but only 23 percent in low-income countries. Gaps also exist between men and women (77 versus 71 percent) and between urban and rural areas (85 versus 58 percent). This pattern is known as the digital divide. Increasingly it involves differences in connection speed, cost and digital skills, as well as whether people have access at all.
Security and reliability. Early protocols were designed for a small community of trusted researchers. They had little built-in protection. Cybersecurity threats include malware, phishing, denial-of-service attacks and the hijacking of routing systems. Encryption protocols such as TLS are now widely used to protect data in transit.
Information quality. It is easy and cheap to publish online. This has expanded access to knowledge, but it also allows misinformation to spread. It raises questions about content moderation, the power of algorithms that rank and recommend content, and, more recently, the effects of generative artificial intelligence on online content.
Energy use. Data centers and networks use a lot of electricity. Demand is growing with the spread of video streaming and artificial intelligence workloads.
References
- ITU's Facts and Figures 2025itu.int
- Statisticsitu.int
- Network Control Protocol (ARPANET)en.wikipedia.org
- ARPANET - January 1, 1983calendarz.com
- Internet Flag Day (1983)centerconsulting.com
- ARPANET Flag Day 1983: Is Not the Birth of the Internetmarknichols.com
- A short history of the Webhome.cern
- Ten years for the public Webrepository.cern