Welcome to the 25th International Summer Institute on Phenomenology of Elementary Particles and Cosmology (SI2019). The Summer Institutes have been held every summer since 1995. It aims at an Aspen-type Institute in Asia. The purpose of the Summer Institute is to promote communications and discussions on research among participants, rather than to give pedagogical lectures for students. Therefore the scientific program is relaxed to keep enough time for discussions. We hope that the new ideas and research activities will be initiated from this institute.