ITRF2008 is an improved version of the International Terrestrial Reference Frame, based on reprocessed solutions of four space geodetic techniques: VLBI, SLR, GPS, and DORIS, spanning 29, 26, 12.5, and 16 years of observations, respectively. The ITRF2008 origin is defined to have zero translations and translation rates relative to the mean Earth center of mass, averaged by SLR time series. Its scale is defined by nullifying the scale factor and its rate relative to the mean of VLBI and SLR long-term solutions. The scale agreement between these techniques is estimated to be 1.05 ± 0.13 ppb at epoch 2005.0 and 0.049 ± 0.010 ppb/yr. The ITRF2008 orientation and its rate are aligned to ITRF2005 using 179 high-quality stations. The origin components from ITRF2008 to ITRF2005 show differences of -0.5, -0.9, and -4.7 mm along X, Y, and Z axes, respectively. The translation rate differences between the two frames are zero for Y and Z, while an X-translation rate of 0.3 mm/yr is observed. The estimated formal errors of these parameters are 0.2 mm and 0.2 mm/yr, respectively. The high level of origin agreement between ITRF2008 and ITRF2005 indicates an imprecise ITRF2000 origin. The ITRF2008 scale accuracy is evaluated to be at the level of 1.2 ppb (8 mm at the equator) over the common time span of the observations. The performance of ITRF2008 is higher than ITRF2005, but future improvements require better consistency between local ties in co-location sites and space geodesy estimates. The ITRF2008 input data include space geodetic solutions and local ties at co-location sites. The ITRF2008 combination strategy involves stacking individual time series and combining them with local ties. The ITRF2008 results show improved precision in station positions and velocities, with WRMS values indicating better performance compared to ITRF2005. The ITRF2008 results also show improved consistency between local ties and space geodesy estimates. The transformation parameters between ITRF2008 and ITRF2005 are estimated using 179 reference stations. The ITRF2008 provides consistent series of polar motion, universal time, and Length of Day, with the latter determined byITRF2008 is an improved version of the International Terrestrial Reference Frame, based on reprocessed solutions of four space geodetic techniques: VLBI, SLR, GPS, and DORIS, spanning 29, 26, 12.5, and 16 years of observations, respectively. The ITRF2008 origin is defined to have zero translations and translation rates relative to the mean Earth center of mass, averaged by SLR time series. Its scale is defined by nullifying the scale factor and its rate relative to the mean of VLBI and SLR long-term solutions. The scale agreement between these techniques is estimated to be 1.05 ± 0.13 ppb at epoch 2005.0 and 0.049 ± 0.010 ppb/yr. The ITRF2008 orientation and its rate are aligned to ITRF2005 using 179 high-quality stations. The origin components from ITRF2008 to ITRF2005 show differences of -0.5, -0.9, and -4.7 mm along X, Y, and Z axes, respectively. The translation rate differences between the two frames are zero for Y and Z, while an X-translation rate of 0.3 mm/yr is observed. The estimated formal errors of these parameters are 0.2 mm and 0.2 mm/yr, respectively. The high level of origin agreement between ITRF2008 and ITRF2005 indicates an imprecise ITRF2000 origin. The ITRF2008 scale accuracy is evaluated to be at the level of 1.2 ppb (8 mm at the equator) over the common time span of the observations. The performance of ITRF2008 is higher than ITRF2005, but future improvements require better consistency between local ties in co-location sites and space geodesy estimates. The ITRF2008 input data include space geodetic solutions and local ties at co-location sites. The ITRF2008 combination strategy involves stacking individual time series and combining them with local ties. The ITRF2008 results show improved precision in station positions and velocities, with WRMS values indicating better performance compared to ITRF2005. The ITRF2008 results also show improved consistency between local ties and space geodesy estimates. The transformation parameters between ITRF2008 and ITRF2005 are estimated using 179 reference stations. The ITRF2008 provides consistent series of polar motion, universal time, and Length of Day, with the latter determined by