ITRF2008 is an improved version of the International Terrestrial Reference Frame (ITRF) based on reprocessed solutions from four space geodetic techniques: VLBI, SLR, GPS, and DORIS. The input data include time series of station positions and daily Earth Orientation Parameters (EOPs). The ITRF2008 origin is defined to have zero translations and translation rates with respect to the mean Earth center of mass, averaged by the SLR time series. The scale is defined by nullifying the scale factor and its rate with respect to the mean of VLBI and SLR long-term solutions. The orientation and its rate are aligned to ITRF2005 using 179 high-quality stations. The ITRF2008 origin accuracy is estimated to be around 1 cm over the SLR observation period, and the scale accuracy is evaluated at 1.2 ppb (8 mm at the equator). The ITRF2008 performance is demonstrated to be higher than ITRF2005, with improved precision in station positions and velocities. The transformation parameters between ITRF2008 and ITRF2005 are also provided for consistency in applications.ITRF2008 is an improved version of the International Terrestrial Reference Frame (ITRF) based on reprocessed solutions from four space geodetic techniques: VLBI, SLR, GPS, and DORIS. The input data include time series of station positions and daily Earth Orientation Parameters (EOPs). The ITRF2008 origin is defined to have zero translations and translation rates with respect to the mean Earth center of mass, averaged by the SLR time series. The scale is defined by nullifying the scale factor and its rate with respect to the mean of VLBI and SLR long-term solutions. The orientation and its rate are aligned to ITRF2005 using 179 high-quality stations. The ITRF2008 origin accuracy is estimated to be around 1 cm over the SLR observation period, and the scale accuracy is evaluated at 1.2 ppb (8 mm at the equator). The ITRF2008 performance is demonstrated to be higher than ITRF2005, with improved precision in station positions and velocities. The transformation parameters between ITRF2008 and ITRF2005 are also provided for consistency in applications.