  As the most ancient branch of astronomy, astrometry has been developed for
thousands of years. However, it has only recently become possible to utilize
astrometry for the detection of exoplanets. Gaia, an astrometric surveyor of 1
billion stars, is capable of measuring the position of stars with a precision
as high as 20 $\mu$as. Gaia is expected to discover more than 10,000 exoplanets
by the end of its mission, surpassing the productivity of most exoplanet
surveys.
  In this chapter, I will introduce different techniques used to achieve
high-precision astrometry. Subsequently, I will explore how both relative and
absolute astrometry can be employed to detect exoplanets. Finally, I will
present the detection limit of the Gaia astrometric survey.
