This monograph summarizes the results of a fifteen-year vascular pathology research project sponsored by the Hungarian Academy of Sciences. The workers who have participated in this project are indebted to the Academy for financing extensive investigations and visits to institutes abroad, the aims of which were to solve certain problems by international cooperation. The results presented by the collective effort of research teams, each studying here have been achieved a particular problem, but working together to the same end. Mutual discussion of findings and a regular exchange of information between the research groups have contributed to the progress of the investigations. Regular pUblication of details and mutual criticism ensured that the findings were uniformly interpreted. It is hoped that the fundamental aim of our long-term project, i. e. the selection of the right approach to the complex problem of vascular pathology, has been achieved. The new approach results from the recognition that since arteriosclerosis finally leads to various kinds of vascular injury, attention should be focussed on the events preceding the development of the lesions rather than on the lesions themselves. This claim has been confirmed by various model experiments in which vascular injury inflicted under different conditions uniformly led to morphologi­ cally verified arteriosclerotic change. The recent increase in the incidence of civi­ lization diseases of the vascular system has resulted in a world-wide expansion of arteriosclerosis research.