Internet capitalization conventions are the standards supported by the various sides involved in the long-standing debate on whether to write "Internet" or "internet".

In formal usage , the word Internet is conventionally treated as a proper noun and written with a capital first letter. Since the widespread deployment of the Internet protocol suite in the early 1980s, the Internet Society, the Internet Engineering Task Force, the Internet Corporation for Assigned Names and Numbers, the World Wide Web Consortium, and several other Internet-related organizations all use this convention in their publications. In English grammar, proper nouns are capitalized, although some analogous things, which are unique yet distributed, such as "the power grid", "the telephone network", and even "the sky", are not considered proper nouns, and arethereforenot capitalized.

Most newspapers, newswires, periodicals, and technical journals also capitalize the term. Examples include The New York Times, the Associated Press, Time, The Times of India, Hindustan Times and Communications of the ACM. The American Psychological Association, in its electronic media spelling guide, capitalizes "Internet."

In other cases, the first letter is often written small (internet).

Since 2000, a significant number of publications have switched to using internet. Among them are The Economist, the Financial Times, The Times (of London), and the Sydney Morning Herald. As of 2005, most publications using internet appear to be located outside of North America although one American news source, Wired News, has adopted the lowercase spelling. Throughout the English-speaking world, including North America, lower-case "internet" is more prevalent than Internet on blogs, personal web pages, and chat rooms.

In the Internet standards community, which includes the IETF, usage historically differentiated between the common noun, with a lower case first letter, and the proper noun, with an upper case first letter. That is, "the Internet" (capital I) referred to the Internet, while "an internet" (lowercase i) referred to any internetwork for connecting multiple networks together - including the use of Internet technologies for this purpose inside private networks. The distinction is evident in a large number of the Request for Comments documents from the early 1980s, when the transition from the ARPANET to the Internet was in progress.

A further example is IBM's TCP/IP Tutorial and Technical Overview (ISBN 0-7384-2165-0) from 1989, which stated that:

The words internetwork and internet is [sic] simply a contraction of the phrase interconnected network. However, when written with a capital "I", the Internet refers to the worldwide set of interconnected networks. Hence, the Internet is an internet, but the reverse does not apply. The Internet is sometimes called the connected Internet.

The Internet-internet distinction fell out of common use after the Internet protocol suite was widely deployed in commercial networks in the 1990s.