My dear friends, I am very pleased and honored to give the opening address in the first Nishinomiya-Yukawa Memorial Symposium on Theoretical Physics. Nishi­ nomiya City wishes to extend a warm and sincere welcome to the many participants here in this Symposium. Nishinomiya is the city where Dr. Hideki Yukawa (1907-1981) was living when he published the famous paper "On the Interactions of Elementary Particles. I" in 1935. For this work he was awarded the Nobel Prize for Physics in 1949. To celebrate the 50th anniversary of his meson theory, our city has started the "Nishinomiya-Yukawa Memorial Activities" to promote the study of theoretical physics, which, we believe, is important for the progress of human society. The annual activities consist of this Symposium, the Nishinomiya­ Yukawa Memorial Prize for promising young physicists and Memorial Lec­ tures for citizens every year. They are conducted by the Steering Committee, the chairman of which is Professor K. Nishijima, the director of the Research Institute for Fundamental Physics, Kyoto University. I would like to express my sincere gratitude to the members of this Committee for their great efforts, as well as to the members of the Organizing Committee of this Symposium. Dr. Yukawa said in his book "Tabibito" ("A traveler" in Japanese), "One who inquires into the truth is just like a traveler without a map." I shall be very happy and proud if this Symposium is successful and provides a useful map for many, particularly for young, physicists.