Two CD‐ROMs containing seismic waveform data obtained from the J‐array Project are now available.The J‐array was a large‐aperture seismic array extending over all of Japan. It consisted of 14 regional seismic networks and more than 200 stations. The project was concerned with detecting small‐amplitude waves that are refracted, reflected, converted, or scattered from seismic velocity discontinuities existing deep within the Earth, and with studying the detailed structure and regional variations of the core, lower mantle, and upper mantle. Continuous digital seismic waveform data were recorded at the rate of 20 Hz with short period seismometers developed under Japan's national program for earthquake prediction. The J‐array project began in April 1991 and continued for 3 years at most of the networks. Many studies have been done with the data, including investigations of the structure of the upper mantle, lower mantle discontinuities, D″ layer, and core. Anyone interested in using the data can refer to J‐array Group [1993] for more information.