This letter is the abbreviated version of an update of the interim report on testing, evaluation, costs, and benefits of advanced spectroscopic portals (ASPs), issued by the National Academies’ Committee on Advanced Spectroscopic Portals in June 2009 (NRC 2009). This letter incorporates findings of the committee since that report was written, and it sharpens and clarifies the messages of the interim report based on subsequent committee investigations of more recent work by the Domestic Nuclear Detection Office (DNDO). The key messages in this letter, which is the final report from the committee, are stated briefly in the synopsis on the next page and described more fully in the sections that follow. The committee provides the context for this letter, and then gives advice on: testing, evaluation, assessing costs and benefits, and deployment of advanced spectroscopic portals. The letter closes with a reiteration of the key points. The letter is abbreviated in that a small amount of information that may not be released publicly for security or law-enforcement reasons has been redacted from the version delivered to you in October 2010, but the findings and recommendations remain intact.