Rockfall occurs not only along the slopes of coastal and mountainous routes but also along the slopes of open pit mines. In this paper, research results and recent techniques concerned with falling behavior of rockfall, simulation methods, prevention measures, detection methods and protection measures are reviewed. It is considered, in general, that the engineering level for rockfall prevention, prediction and protection methods in Japan are not handicapped compared with those of Switzerland and other countries. However, accumulation of the data concerned with motion characteristics of rockfall is not so sufficient in Japan. Further tests on the motion characteristics of rockfall are expected to be continued because validity of simulation and other prevention and protection works can be confirmed only with reference to those field data. In the latter half of this paper, rock net system was discussed as an useful protection measure against rockfall. Ling net system which was developed in Switzerland is currently used as an effective mitigation method against rockfall energy in European Countries and high performance of the net has been tested also in Japan recently importing from Switzerland. It is considered that research works should be carried out intensively to develop other mitigation method of high performance against rockfall energy, not only because large amount of protection net is used every year in our country but also because the patent for the ling net was granted already in Switzerland. 543〈 1 〉