Urban seismic risk is rapidly increasing, particularly in developing countries, where a number of mega-cities are growing.Almost half of the world population lives in cities, where all kinds of human activities are concentrated. Thus, cities are more and more vulnerable to disasters, particularly to earthquakes, which can strike any city suddenly without warning. Once an earthquake takes place in a large city,the damage can be tremendous both in human and economic terms. Even an intermediate earthquake can cause destructive damage to a city as in the cases of the 1995 earthquake in Kobe. Japan and the 1999 earthquake in Kocaeli,Turkey. There is a tendency to think that disaster prevention would cost much more than relief activities. However, the reality is the reverse. Our society has been spending a lot of resources for response activities after disasters; these resources could have been drastically reduced if some had been spent for disaster prevention.There is also a tendency to look at disasters mainly from a humanitarian angle, bringing us into the position of giving priority to the response to disasters. However, relief activities can never save human lives that have already been lost. Response activities can never help immediately resume functions of an urban infrastructure that have already been destroyed. The bottom line is that buildings should not kill people by collapsing and infrastructure should not halt social and economic activities of the city for a long time. It is essential particularly for seismic risk reduction to concentrate our efforts on prevention and preparedness.The secretariat of the lnternational Decade for Natural Disaster Reduction (IDNDR 1990-2000), United Nations, Geneva, therefore, launched the RADIUS (Risk AssessmentTools for Diagnosis of Urban Areas against Seismic Disasters) initiative in 1996, with financial assistance from the Government of Japan. It aimed to promote worldwide activities for reduction of seismic disasters in urban areas, particularly in developing countries.