Honinbō (本因坊, Hon'inbō) was the name of one of the four major schools of Go in Japan. Easily the strongest school of Go for most of its existence, it was established in 1612 and survived until 1940.
Upon the closure of the school, the title Hon'inbō came to be used for the winner of the Honinbo Tournament, which is now an annual professional go event in Japan. It is run under the titleholder system, meaning that at any given time there is a player who can use the title Hon'inbō. It is customary for Japanese players to take a special personal name as Hon'inbō, a unique feature of this title; for example Takagawa Kaku held the title for nine years, and during this time was referred to as Honinbō Shukaku. Players of other nationalities by custom do not adopt a special name, but do use the Hon'inbō title.
Another prominent member was Honinbo Shusaku (秀策, 1829-1862), who was heir to be head of the school, but died of cholera first.
All three of the "go saints" (or Kisei) came from this school - Dosaku, Shusaku and Jowa (although Jowa is frequently reviled because of his machinations while trying to become Meijin). Most of the holders of the Meijin title (awarded to a player recognised by all as strongest) were also from this house.
The Nihon Ki-in decided to name players who had won the Honinbo tournament 5 times or more in a row (making them Honorary Honinbo) would be given the Honinbo prefix after Cho Chikun won the title 10 times in a row. This meant that Takagawa Kaku (9 in a row), Sakata Eio (7), Ishida Yoshio (5), and Cho Chikun (10) may be addressed as 22nd, 23rd, 24th and 25th Honinbo respectively whether or not they are currently holding the Honinbo title.