The first GNSS (Global Navigation Satellite System) CORS (Continuously Operating Reference Station) in Estonia became operational in 1996. Starting from 2008 four Estonian CORS are incorporated into the EPN (EUREF Permanent GNSS Network). During the years 2014-2015 modernization of the GNSS CORS in Estonia was carried out. Currently the total number of the resulting ESTPOS reference stations is 28. These ESTPOS stations were interconnected to the I order national geodetic network by a special GNSS campaign in 2017. The maintenance and compilation of the ESTPOS based research products is explained. Aspects of the ESTPOS usage, including also the real time surveys, are discussed. Comparisons with SWEPOS (Swedish national GNSS CORS) and FinnRef (Finnish national GNSS CORS) networks indicate possibilities for further ESTPOS developments.