  Magnetic field in the solar lower atmosphere can be measured by the use of
the Zeeman and Hanle effects. In contrast, the coronal magnetic field well
above the solar surface, which directly controls various eruptive phenomena,
can not be precisely measureed with the traditional techniques. Several
attempts are being made to probe the coronal magnetic field, such as force-free
extrapolation based on the photospheric magnetograms, gyroresonance radio
emissions, and coronal seismology based on MHD waves in the corona. Compared to
the waves trapped in the localized coronal loops, EIT waves are the only
global-scale wave phenomenon, and thus are the ideal tool for the coronal
global seismology. In this paper, we review the observations and modelings of
EIT waves, and illustrate how they can be applied to probe the global magnetic
field in the corona.
