Japan is covered by an extensive and reliable network of railways. 70% of this is owned and operated by the Japan Railway Group, more commonly known as JR Group (JRグループ). This consists of six passenger railway companies of JR Hokkaido, JR East, JR Central, JR West, JR Shikoku, and JR Kyushu, and one nationwide freight railway company. Together they operate a nationwide network of regional and local train lines including Shinkansen (新幹線).
The remaining 30% belongs to other private railway companies mainly in urban and suburban routes such as Tokyo and Osaka areas. Note that you cannot use JR Pass on these lines.
Here you can find information on all 6 JR groups. read more