This volume contains the papers presented at the Second International Conf- ence on Discovery Science (DS 99), held in Tokyo, Japan, December 6-8, 1999. The conference was colocated with the Tenth International Conference on Al- rithmic Learning Theory (ALT 99). This conference was organized as part of the activities of the Discovery S- ence Project sponsored by Grant-in-Aid for Scienti c Research on Priority Area fromthe MinistryofEducation, Science, SportsandCulture (MESSC)ofJapan. This is a three-year project starting from 1998 that aims to (1) develop new methods for knowledge discovery,...