THE ILLEGAL USE OF EXPLOSIVES IS AN AREA OF INCREASING CONCERN AMONG ALL LAW ENFORCEMENT GROUPS IN THE UNITED STATES. TECHNICAL DEVELOPMENT OF INSTRUMENTS AND TECHNIQUES TO ASSIST IN THE CONTROL OF THE ILLEGAL USE OF EXPLOSIVES ARE BEING ACTIVELY PURSUED UNDER THE SPONSORSHIP OF MANY GOVERNMENT AGENCIES. IT IS NOTED THAT MAJOR EFFORTS TO DATE HAVE BEEN EXPENDED TO SOLVE THE PROBLEM OF UNTAGGED DETECTION OF EXPLOSIVES IN CONTROLLED-ACCESS SCENARIOS WHERE SPEED OF DETECTION IS A MAJOR FACTOR. VAPOR-CHARACTERIZATION STUDIES PROVIDE ESSENTIAL INFORMATION ON THE PRACTICAL LIMITATIONS OF VAPOR DETECTION. THE AUTHORS STATE THAT VAPOR DETECTION TECHNIQUES BEING PURSUED INCLUDE ELECTRON CAPTURE METHODS, ENZYMATIC REACTION, AND OPTICAL METHODS SUCH AS LASER PHOTOACOUSTICS. PHYSICAL METHODS DISCUSSED IN THIS REVIEW INCLUDE THERMAL NEUTRON CAPTURE, X-RAY IMAGING, AND NUCLEAR MAGNETIC RESONANCE. DETECTION TAGGING METHODS EXAMINED IN THIS ARTICLE INCLUDE VAPOR TAGGING AND OTHER EXPERIMENTAL METHODS SUCH AS HEAVY METAL TAGGANTS. FINALLY, IT IS NOTED THAT DEVELOPMENT OF IDENTIFICATION TECHNIQUES USING RARE-EARTH AND COLOR-CODED TAGGANTS HAS REACHED THE ADVANCED DEVELOPMENT STAGE AND THAT EVALUATION OF NEW RESIDUE CHARACTERIZATION TECHNIQUES FOR UNTAGGED CASES HAS ALSO BEEN COMPLETED. (AUTHOR ABSTRACT MODIFIED)...DMC