A few of large scale mudflow occur in mountainous regions a year in Japan, then damage results to roads, buildings and other works of man and affects often people's lives. Hence, in order to get methods of prediction and control of mudflow, various investigations on the phenomena have been carried out.
In this report, many papers of the investigations were collected, and mainly summarized in order to examine the present state of understanding of the phenomena and to advance effective investigations in the future. Following points are deeply concerned, as part (I), which are definition, classification, nature of flowage, deposition and (topographical and geological) conditions of occurrence of mudffow.