For many Earth science applications as well as for satellite navigation, geodesy has the potential to provide a Terrestrial Reference Frame (TRF), to which are related valuable observations of parameters that govern the Earth system: Earth Rotation and its gravity field, tectonic motion, crustal deformation, post-glacial rebound, sea level variation, geocenter motion, etc. While any individual space geodesy technique (VLBI, SLR, DORIS, GNSS including Galileo in the future) is able to provide all the necessary information of the TRF datum definition (origin, scale, orientation and its time evolution), combination of reference frames provided by independent techniques has long been the standard method to implement the International Terrestrial Reference Frame (ITRF). In principle, the particular strengths of one observing method can compensate for weaknesses in others if the combination is properly constructed, suitable weights are found, and accurate local ties in co- location sites are available. The prerequisite for precise quantification of parameters describing the geophysical phenomena of the changing planet, with direct implications to water cycles, ice sheets, sea level rise, climate change, global warming and geohazards, is the availability of numerous, globally distributed, and continuously observing space geodesy instruments that constitute the main foundation of the ITRF. This paper tries to illustrate the major ITRF achievements, applications and recent results based on time series (weekly from satellite techniques and daily from VLBI) of station positions and Earth Orientation Parameters, being the current ingredients of the ITRF realization. Pertinent results will be shown to demonstrate the benefits of time series that allow to monitor and quantify Earth's rotation, station non-linear motion, seasonal variations, displacements due to earthquakes, post-glacial rebound and other types of crustal deformation.