  The International VLBI Service for Geodesy & Astrometry (IVS) regularly
provides high-quality data to produce Earth Orientation Parameters (EOP), and
for the maintenance and realization of the International Terrestrial and
Celestial Reference Frames, ITRF and ICRF. The first iteration of the celestial
reference frame (CRF) at radio wavelengths, the ICRF1, was adopted by the
International Astronomical Union (IAU) in 1997 to replace the FK5 optical
frame. Soon after, the IVS began official operations and in 2009 there was a
significant increase in data sufficient to warrant a second iteration of the
CRF, ICRF2. The most recent ICRF3, was adopted by the IAU in 2018. However, due
to the geographic distribution of observing stations being concentrated in the
Northern hemisphere, CRFs are generally weaker in the South due to there being
fewer Southern Hemisphere observations. To increase the Southern Hemisphere
observations, and the density, precision of the sources, a series of deep South
observing sessions was initiated in 1995. This initiative in 2004 became the
IVS Celestial Reference Frame Deep South (IVS-CRDS) observing program. This
paper covers the evolution of the CRDS observing program for the period 1995 to
2021, details the data products and results, and concludes with a summary of
upcoming improvements to this ongoing project.
