  We report on recent refinements and the current status for the rotational
state models and the reference frame of the planet Mercury. We summarize the
performed measurements of Mercury rotation based on terrestrial radar
observations as well as data from the Mariner 10 and the MESSENGER missions.
Further, we describe the different available definitions of reference systems
for Mercury, which are realized using data obtained by instruments on board
MESSENGER. In particular, we discuss the dynamical frame, the principal-axes
frame, the ellipsoid frame, as well as the cartographic frame. We also describe
the reference frame adopted by the MESSENGER science team for the release of
their cartographic products and we provide expressions for transformations from
this frame to the other reference frames.
