Based on the experiences of projects in the field of conversion, the hazards typically associated with different conversion sites such as former military training areas, air fields, barracks, bunkers and fortifications, depots, battlefields, armament factories, explosives production facilities and chemical warfare agent production facilities are presented. Then, strategies for the historic investigation of former military sites and sources of information including historic maps, aerial photographs, archival records, eye witness interviews, analysis of contemporary literature, military specifications and service regulations are discussed with respect to their utilisation and acquisition from different archives and libraries and their value as sources of historic information. Finally, the combination of single pieces of historic information into a mosaic depicting a near-complete image of activities at former military sites and its application for risk assessment are considered.