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While there currently are a number of effective technologies and methodologies for explosive screening when close proximity to the person, package, or vehicle being screened is feasible, the problem of detecting explosives at significant standoff distances remains one of the most difficult - and most important - challenges confronting physical security specialists. Among the major detection techniques, trace detection suffers from the fact that available vapor plumes are normally too dilute for detection at appreciable standoff under all but the most favorable conditions, and probing bulk techniques suffer from an intrinsic 1/r4 fall-off of the signal intensity with distance. Research into potential means of standoff detection is necessary to try to address this important problem. This paper presents an overview of detection technologies that could prove useful in certain standoff detection applications, along with comments on future research needs. A distinction is made between remote detection, in which the personnel searching for explosives maintain a safe standoff distance from the object being screened but where a sampling and/or detection unit may approach the object closely, and true standoff detection, where both the personnel and the sampling/detection equipment maintain a large standoff distance.