The Bingo Book is a book that contains any and all information on every rogue ninja, which all Jonin, Arunin, and members of the ANBU of the major shinobi villages are given by their respective Kage to hunt down and assassinate. The purpose of this is so that village's secret and/or kekkei genkai aren't stolen or examined by the enemy. Kirigakure has a special unit within their ANBU called the Tracker Ninja, whose sole purpose is the complete eradiction of these rogue ninja.