Since the discovery of x rays by Roentgen in 1895, a progression of reports containing recommendations to reduce the hazards from this "invisible light" have been published. These reports, generated by a number of expert national and international bodies, issued ever-evolving protection guidelines for shielding radiation workers and members of the public from the potential health effects of this radiation. In recent years, significant changes have been made in the recommended dose limits, and a number of articles that provide updated shielding data, parameters, and methodologies for x-ray imaging facilities have been published. Scientific Committee 9 (SC9) of the National Council on Radiation Protection and Measurements (NCRP) (formed with the support of the American Association of Physicists in Medicine), was given the charge of reviewing the literature and updating the NCRP shielding recommendations for x rays used for medical imaging purposes (i.e., for diagnostic and interventional procedures). This article focuses on the new data and models presented in these recent publications and on the recommendations of the current NCRP report, produced by SC9, for the design of radiation barriers in medical imaging facilities.