Description:This book constitutes the refereed proceedings of the Second International Conference on Discovery Science, DS'99, held in Tokyo, Japan, in December 1999.The 26 revised full papers presented together with 2 invited contributions and 25 poster presentations were carefully reviewed and selected from a total of 74 submissions. The following topics are covered in their relation to discovery science: logic, inference, algorithmic learning, heuristic search, database management, data mining, networking, inductive logic programming, abductive reasoning, machine learning, constructive programming, intelligent agents, statistical methods, visualization, HCI, etc.