Recently, an area of research dealing with the threat of Intentional Electromagnetic Interference (IEMI) specifically directed against transmission and distribution of electric power has been established at a Swedish civilian research centre called High Voltage Valley (HVV). One reason for the increased attention is a couple of reports from the U.S. alarming that an attack using a nuclear weapon generating a High-Altitude EMP (HEMP) is possible to carry out even for terrorists. The HEMP may create very severe effects on the infrastructure, especially on the electric power grid. Also in Europe HEMP, but especially the threat from portable sources such as High Power Microwave (HPM) sources, has been pointed out as a threat. This report sums up research initiatives at HVV to build up knowledge to forecast the response of the power transmission and distribution system when subjected to an IEMI attack and to apply methods of protection.