NOAA’s National Geodetic Survey recently released version 3.1 of its Horizontal Time-Dependent Positioning (HTDP) utility for transforming coordinates across time and between spatial reference frames. HTDP 3.1 introduces improved crustal velocity models for both the contiguous United States and Alaska. The new HTDP version also introduces a model for estimating displacements associated with the magnitude 7.2 El Mayor – Cucapah earthquake of April 4, 2010. In addition, HTDP 3.1 enables its users to transform coordinates between the newly adopted International Terrestrial Reference Frame of 2008 (ITRF2008) and other popular reference frames, including current realizations of NAD 83 and WGS84. With HTDP 3.1, users can now employ a new, more convenient format to transform coordinates for multiple locations, as well as enter times in both the decimal-year format and the month-day-year format. The new HTDP utility, plus instructional material, are available at www.geodesy.noaa.gov/TOOLS/Htdp/Htdp.shtml. For more information, contact Chris.Pearson@noaa.gov.