  2019 marked the 20th anniversary of the International VLBI Service for
Geodesy and Astrometry (IVS). This service is the largest and most
authoritative organization that coordinates international activities in radio
astrometry and VLBI sub-system of space geodesy. Currently, about 60 antennas
located in many countries on all continents participate in the IVS observing
programs. The IVS Data Centers have accumulated more than 18 million
observations obtained during more than 17'000 sessions, including more than
10,000 Intensive sessions for rapid determination of Universal Time. The paper
traces the dynamics of IVS development based on statistical processing of the
array of observations collected in the IVS Data Centers for the period of
1979-2018. Various statistics by the years, stations, baselines, and radio
sources are provided. The evolution of the IVS observational data and the
accuracy of results obtained from processing VLBI observations is considered.

Instrumentation and Methods for Astrophysics