  The astrometry technique is an important tool for detecting and
characterizing exoplanets of different type. In this review, the different
projects which are either operating, in construction or in discussion are
presented and their performance discussed in the framework of the Blue Dots
study. We investigate the sensitivity of astrometry to different sources of
noise and we show that astrometry is a key technique in the path of discovering
and characterizing new types of planets including the very challenging category
of Earth-like planets orbiting the habitable zone of solar-type stars.
