The results of the joint researches by utilizing the facilities of JAERI in 1991 fiscal year were summarized, and this report was able to be completed. Many researchers in whole Japan took part in many themes, and the very significant results were obtained. Now this joint research has reached the great turnabout period. The reconstructed JRR-3M was offered for joint utilization since April, 1991, and the utilization for neutron diffraction and scattering increased largely. As for the ion irradiation facility in Takasaki Research Establishment, the partial operation will be started in the next year, and the joint utilization is expected to begin. Accompanying the diversification of the utilization of facilities, in order to properly meet the needs of users, the thorough revision of the system seems necessary. The number of research themes in 1991 was 222 cases. JRR-3M accomplished the joint utilization operation of 8 cycles as expected, but JRR-2 caused a trouble during 5th cycle, and the operation thereafter was canceled. In this book, 159 reports are collected. (K.I.).