Abstract: A book stiffener of a type having a relatively flat, thin, elongated, rigid rotatable-strip (32) attached by a swivel mechanism (34, 108) to an outside surface of a book cover, also includes an indexing mechanism between the rotatable strip and the book cover for holding the rotatable strip in predetermined angular index positions relative to the book cover. The index positions include a stiffening position in which the rotatable strip extends across hinge seams (24, 26) of front and rear flap covers (18, 20) of the book cover, and a disabled position in which the rotatable strip extends more nearly parallel with a back binding (22) of the book cover so as not to substantially extend across the hinge seams. The indexing mechanism includes protrusions (102, 122) on one of the book cover and the rotatable strip and indentations (104, 124) on the other of the book cover and the rotatable strip, with a protrusion resiliently snapping into an indentation at the index positions.