There are two principal religions in Japan, Shintoism and Buddhism, officially followed by 54% and 40% of the population respectively.
Shintoism is more a set of traditions and customs than an actual religion. It is classified as an animist religion as people believe in the spirits of nature, or kami, which can be found in a tree, a rock or a waterfall. Shintoists are not bound by any formal set of rules, such as the Bible in Christianity of the Koran in Islam.
Japanese Buddhism is divided in 15 sects, although only 7 of them are still relatively common nowadays.
Japanese people are not very religious, with greatest part of the population only visiting temples for the New Year. The Japanese also do not mind mixing elements of Buddhism and Shintō with one another, and many people would be at a loss to say which element belongs to which religion (=> see Temples & shrines : an explanation).
There is a Christian minority in Japan, dating back from the contact with Portuguese and Spanish missionaries in the 16th century. Christians only make up 1% of the Japanese population, and most are to be found in Kyushu, especially in Nagasaki
There are only a few thousands Muslims residing in Japan. All of them are immigrants from Muslim countries, mostly Indonesia, Malaysia, Bangladesh, Pakistan, Iran and Turkey (=> see Registered Foreigners in Japan by Nationality), or recent Japanese converts who married them.
The 20th century has seen the emergence of new cults, many of which are based on Shintō and/or Buddhist beliefs. The most influencial of them is Soka Gakkai, a form of the Buddhism of Nichiren Daishonin founded in 1930. It now has several millions followers in Japan and is related to the political party Komeitō ("Clean Government Party").
New religious groups have not always cohabtited peacefully with the rest of the population, as showed the 1995 sarin gas attack in the Tokyo underground, perpetrated by members of the religious group Aum Shinrikyo.