A new realization of the International Celestial Reference Frame (ICRF) is presented based on the work achieved by a working group of the International Astronomical Union mandated for this purpose. This new realization follows up on the initial realization of the ICRF completed in 1997 and its successor adopted as a replacement in 2009.

The new frame, referred to as ICRF3, incorporates nearly 40 years of data acquired by Very Long Baseline Interferometry at the standard geodetic and astrometric radio frequencies (2.3 and 8.4 GHz) along with additional observations collected at higher radio frequencies (24 GHz and dual-frequency 8.4/32 GHz) over the past 15 years. State-of-the-art astronomical and geophysical modeling has been used to analyze these data and derive source positions. The modeling integrates for the first time the effect of the Galactocentric acceleration of the Solar System which, if not considered, produces significant deformation of the frame due the time range of the data. 

ICRF3 contains positions for 4536 extragalactic sources, as measured at 8.4 GHz, 303 of which, uniformly distributed on the sky, are identified as defining sources and as such serve to define the axes of the frame. Positions at 8.4 GHz are supplemented with positions at 24 GHz for 824 sources and at 32 GHz for 678 sources. In all, 600 sources have three-frequency positions available. The positions have been estimated independently at each of the frequencies in order to preserve the underlying astrophysical content behind such positions. The frame is aligned onto the International Celestial Reference System to within the accuracy of ICRF2. Positions are reported for epoch 2015.0 and must be propagated for observations at epochs away from that epoch, accounting for a Galactocentric acceleration of 0.0058 mas/yr, for the most accurate needs. Individual source coordinates have a noise floor of 0.030 mas. 

ICRF3 is the new fundamental celestial reference frame adopted by the International Astronomical Union at its XXXth General Assembly (20-31 August 2018) as a replacement of ICRF2 as of 1 January 2019.