Internet in Japan provides high quality services to more than 90% of the population and almost 100% of medium to large businesses, with mobile Internet on devices like smartphones being the most popular type of service. The Ministry of Internal Affairs and Communications (MIC) oversees the telecommunications, Internet, and broadcast sectors, but regulation of Japan's Internet industry is largely through voluntary self-regulation. There is little or no explicit censorship or restriction of Internet content, with the government respecting laws for freedom of speech and of the press, but there are concerns that the government indirectly encourages self-censorship practices. The Internet in Japan is not a singular medium and affects Japanese culture in a variety of ways as diverse groups of Japanese people interact online.

Self-regulation plays an important role among Japanese Internet Service Providers (ISP), as Japan lacks an independent regulatory commission. The Ministry of Internal Affairs and Communications (MIC) oversees the telecommunications, Internet, and broadcast sectors with a hands-off approach. Law enforcement is more proactive in regulation of the internet and has made arrests with mixed results on the basis of online activity. Non-profit organizations such as the Broadcasting Ethics & Program Improvement Organization have been formed to help regulate the Internet.

Japan has three major mobile operators—au by KDDI, NTT's DoCoMo, and Softbank. NTT, while considered a privatized and reorganized ex-state monopoly, remains dominant in practice due to the expense of switching providers, the inconvenience of changing contact information, and other causes tying customers to dominant operators. While the market is open, the NTT group remains dominant and the Japanese government is still the mandated largest shareholder of NTT. The government owns a third of the company, enough to control the vote at shareholder meetings. The government has not exercised this power to manage the company and may have little incentive to challenge NTT's market dominance and push for more competition because of the returns it gets from being a shareholder. No major foreign firms have successfully entered the market, with the exception of smartphones by Apple and Samsung.

In September 1984, Jun Murai connected Keio University and Tokyo Institute of Technology with a 300 bit/s line using a telephone line instead of the physical delivery of tape media. In October of the same year, the University of Tokyo was connected and expanded to JUNET, which became the basis of the internet in Japan.

In Japan, Nippon Telegraph and Telephone (NTT) planned ^[when?] a step-up process from dialup 56 kbit/s ISDN 64 kbit/s, to fiber to the premises (FTTP). Under this plan, NTT had been selling ISDN products primarily toward home users while corporate customers sometimes skipped ISDN entirely and immediately upgraded to the still-expensive fiber to the home (FTTH) service. In the late 1990s, cable television operators began offering their own cable broadband products, but relatively high initial installation costs and cheaper alternatives limited its spread.^{[citation needed]}

In 1999, NTT DoCoMo pioneered the world's first large-scale mobile Internet service, iMode. It was at this time that the Japanese public began to take interest in the Internet. Notably, this means that the Japanese public started with mobile Internet services rather than Internet through personal computers. It is argued that the complexity of the Japanese scripts largely contributes to the lesser popularity of PC Internet. Today, typing in Japanese often involves typing a series of characters and converting them into Kanji (Chinese characters), which can be a slow process. Therefore, typing on a computer would not result in a significant speed advantage over mobile devices, taking away an important feature of computers. Those against this view claim that it is complicated by the popularity of word processors in Japan, which would have the same issue as computer keyboards. By 1993, 37.8% of Japanese households owned stand-alone word processors, while only 11.9% of households owned personal computers. Alternatively, it is suggested that Internet through personal computers is less popular due to the presence of substitutes for popular computer functions: word processors for documentation, cell phones with iMode mobile Internet for communication, game consoles for entertainment.

Asymmetric digital subscriber line (ADSL) services were started by a venture company, Tokyo Metallic in 1999. After this NTT started and some other companies followed. In 2001, SoftBank started a 12 Mbit/s ADSL service. It was a shocking event because the price was around only 3,000¥ (30US$), which was half the cost of other companies. This, coupled with aggressive marketing campaigns led to their capturing of large shares of the market. Competitors and Softbank each dropped prices in a price war and repeatedly readied higher-speed services to entice customers (12 Mbit/s/s 24 Mbit/s/s, 50 Mbit/s). In 2004, Japan had the best cost to performance ADSL service in the world (50 Mbit/s, 35US$) which it held on to in the successive years.

At the same time, NTT and electric power companies expanded FTTP areas. In most urban areas, people can use FTTP (100 Mbit/s, 50US$), but ADSL is still mainstream. However, large discounts and free installation have boosted FTTP adoption. Many new apartments are built to accommodate this service with little or no wiring. In 2005, Kansai Electric Power launched a 1 Gbit/s FTTH service at 8700yen (90US$).^{[citation needed]}