These proceedings contain the presentations and results of several discussions of the workshop on “Detection and Disposal of Improvised Explosives” held in St.-Petersburg, Russia, September 7-9, 2005. This Advanced Research Workshop was the fourth event concerning Detection of Explosives in connection with counter terrorism. After the first three workshops, dealing with vapor and trace detection, electronic nose detection and detection of bulk explosives, this workshop was devoted to the detection of Improvise Explosives including: Methods of detection of Improvised Explosives (IE). Methods of detection of Improvised explosives devices (IED). Disposal and safe handling of ID and IED. The treatment of detection methods may be divided in the following groups: Overview about the different methods; Trace- and vapor detection; Electromagnetic methods; Neutron methods; Laser techniques. Because of different definitions of Improvised Explosives the parti- pants of the workshop agreed after some discussions with the following definition: An Improvised Explosive (IE) can be any chemical compound or mixture capable of an explosive reaction. They are normally easily prepared by a knowledgeable layman under simple conditions. Components of IE are typically inorganic salts containing molecular bound oxygen like nitrates, chlorates or perchlorates etc. or organic compounds with nitro-, nitami- or nitrate-groups or peroxides. Admixtures of military or commercial explosive materials are also used. From the chemical point of view IE can be divided into the following types: Salts containing chemical groups with oxygen (like nitrates, chlorates or perchlorates etc.) in mixtures with combustible substances like carbon-hydrogen compounds.