"Fushinjo" is considered to be Kukai's masterpiece, the same as "Kukai Kanjo rekimei" (Register of Participants in Esoteric Consecration Ceremony); an edition of three volumes, "Fushinjo" (Volume one), "Kotsuhijo" (Volume two), "Kotsukeijo" (Volume three), was assembled into one volume, but the name came from their first edition.
『風信帖』は、『空海灌頂歴名』と並び称せられる空海の書の最高傑作であり、『風信帖』（1通目）、『忽披帖』（2通目）、『忽恵帖』（3通目）の3通を1巻にまとめたもので、その1通目の書き出しの句に因んでこの名がある。