Countries around the world are deploying radiation portal monitor systems to interdict the illicit shipment of radioactive material crossing international borders. Because of their high efficiency for gamma-ray detection, most deployed systems are based on plastic scintillators and are non-spectroscopic in capability. Spectroscopic portal monitor systems are undergoing engineering development for near term deployment. The ability to identify the detected radionuclides may allow improved operational handling of radiation alarms, particularly those from the normal commerce of naturally occurring radioactive material. The goal for improved systems is to increase the sensitivity to threats while reducing the operational impact of nuisance alarms.