This classic samurai-era text fused Japanese swordsmanship with Zen and influenced the direction that the art has taken ever since. Written by the seventeenth-century Zen master Takuan Soho (1573–1645), The Unfettered Mind is a book of advice on swordsmanship and the cultivation of right mind and intention. It was written as a guide for the samurai Yagyu Munenori, who was a great swordsman and rival to the legendary Miyamoto Musashi.

Takuan was a giant in the history of Zen; he was also a gardener, calligrapher, poet, author, adviser to samurai and shoguns, and a pivotal figure in Zen painting. He was known for his brilliance and acerbic wit. In these succinct and pointed essays, Takuan is concerned primarily with understanding and refining the mind—both generally and when faced with conflict. The Unfettered Mind was a major influence on the classic manifestos on swordsmanship that came after it, including Miyamoto Musashi's Book of Five Rings and Yagyu Munenori's Life-Giving Sword.