Ben Kenobi's book was a tome found by Luke Skywalker in Ben Kenobi's hut in 3 ABY. It was left by Obi-Wan Kenobi for Luke Skywalker and contained enormous amount of information useful for the young Jedi, including the plans for building a lightsaber as well as instructions for building the required tools to do so. Skywalker made use of it to contruct his own lightsaber.
The volume the book was being kept in, was locked by a thumbprint clasp, that could be opened by Skywalker's thumbprint only and was rigged with a flashpacket to burst into flames had anyone else tried to open it.