This is the twenty-fifth edition of Reference Data Series No. 2, which presents the most recent reactor data available to the IAEA. It contains summarized information as of the end of 2004 on: (1) power reactors operating or under construction, and shut down; and (2) performance data on reactors operating in the IAEA Member States, as reported to the IAEA. The information is collected by the IAEA through designated national correspondents in the Member States. The replies are used to maintain the IAEA's Power Reactor Information System (PRIS).