The second realization of the ICRF with VLBI

The ICRF derived from VLBI observations of extragalactic radio sources up to 1995.6 and effective since 1998.0 was a radical change from the FK5 stellar/equinox celestial system. Since then the number of geodetic/astrometric VLBI observations has tripled and the number of radio sources with astrometrically useful data has quadrupled. These data along with advances in modeling and estimation will be used to generate the next ICRF realization in the microwave band. Analysis of source position time series and source structure evolution will be used to select better "defining" sources. Working groups have been established by the IAU, IERS and IVS with the goal of presenting the second realization of the ICRF at the IAU General Assembly in 2009.