The Big Four law firms (四大法律事務所, yondai hōritsu jimusho) or the Big Four (四大, yondai) is a term informally used in Japan to refer to those firms which, collectively, are perceived to be the largest firms headquartered in Japan and distinguished in comparison to their other competitors.
The Big Four firms are:[1][2] Nowadays, the term "Big Five" is sometimes used to include the fifth-largest firm in Japan by number of lawyers, TMI Associates.
[3] On the other hand, overseas commentators have used "Big Five" to include Atsumi & Sakai[4].A 2023 overall ranking of Japanese law firms by Top Ranked Legal also rated Atsumi & Sakai fifth following Mori Hamada & Matsumoto, Anderson Mori & Tomotsune, Nishimura & Asahi, and Nagashima Ohno & Tsunematsu.
During the years immediately following World War II, several American lawyers established such firms in Japan (e.g. Anderson Mori).
Japanese lawyers with international training began establishing international firms in the 1960s, and since regulatory changes in the 1990s, many Japanese lawyers have joined or partnered with Tokyo offices of major multinational law firms.