This volume is the Proceedings of the Third Korea-China-Japan Inter- national Symposium on Ring Theory held jointly with the Second Korea- Japan Joint Ring Theory Seminar which took place at the historical resort area of Korea, Kyongju, June 28-July 3, 1999. It also includes articles by some invited mathematicians who were unable to attend the conference. Over 90 mathematicians from 12 countries attended this conference. The conference is held every 4 years on a rotating basis. The first con- ference was held in 1991 at Guilin, China. In 1995 the second conference took place in Okayama,...