Wasan means an anthem sung in Japanese to praise Buddha, Bosatsu, Soshi (founder of a sect), ancient virtue, Buddhist scriptures, creed, etc. This is a counterpart to bonsan (Sanskrit hymns) chanted in Sanskrit, or Kansan chanted in ancient Chinese. Many of the Wasan were made in poems of the seven-five syllable style, and were chanted with the intonation that was popular in the period when the Wasan was made.
The oldest Wasan was made in the Heian period, and there were popular Wasan called 'Hokke santan' and 'Momosaka sandan.'
Such old Wasan included 'Hongakusan' which is said to have been made by Ryogen, 'Gokurakujodo Mida wasan' made by Senkan (Dento Daihosshi), 'Gokuraku rokuji san' and 'Raigo san' made by Genshin (a monk). Most of of them became popular with the Tendai Jodo sect in the middle of the Heian period.
In the Kamakura period, Wasan was widely recognized with the propagation of Buddhism, and became popular in various sects of Kamakura Bukkyo (new Buddhist movements of the Kamakura Period). Famous Wasan were 'Sanjo wasan' (three Buddhist verses) (Jodo-wasan, Koso-wasan, Shozomatsu-wasan) made by Shinran, the founder of the Jodoshinshu sect (True Pure Land Sect Buddhism), 'Jogo Wasan' including 'Betsugan san' by Ippen of the Jishu sect and 'Ojo san' by Taa.
Such Wasan chants became widely influential among ordinary people and affected Japanese music greatly; their effect can be still found in the singing methods of Minyo (traditional folk songs), songs and ballads, especially Enka (Japanese ballad).