The issue of missile defense cooperation with Japan intersects with several issues of direct concern to Congress, ranging from support for developing a capability to protect U.S. regional forces, Asia-Pacific allies, and Taiwan, from Chinese short- and medium-range missiles, to countering a possible future threat to U.S. territory from long-range missiles developed by North Korea. Japan's current participation in the U.S. ballistic missile defense (BMD) program dates from August 1999, when the Japanese government agreed to conduct cooperative research on four components of the interceptor missile being developed for the then U.S. Navy Theater-Wide (NTW) anti-missile system a sea-based "upper tier" (exo-atmospheric) capability against short- and medium-range missiles up to 3,500 kilometers. In the spring of 2001, the Administration changed the context of the cooperative research effort when it reorganized and redirected the U.S. missile defense program to emphasize the employment of specific technologies across the entire spectrum of missile defense challenges, but especially to gain a limited, near-term capability to defeat missile attacks on U.S. territory by "rogue" states. The Pentagon redesignated the NTW program as the Sea-Based Midcourse System, with a goal of developing a capability for attacking missiles of all ranges in the initial or middle phases of their flight path. This change added to an already complex list of Japanese policy concerns, by putting Japan in the position of possibly cooperating in the development of technology that could become part of an American national missile defense capability a step that many Japanese see as transgressing a constitutional ban on "collective defense." Thus far, the Administration's program change has not deterred Japan from cooperative research on missile defense, but the policy shift has unsettled Japanese leaders and created additional political obstacles to bilateral BMD cooperation. The new U.S. approach has been criticized in the Japanese press and the Diet (parliament), both because of the potential violation of the implied ban on "collective defense" contained in Article 9 of Japan's U.S.-imposed "Peace Constitution," and also because the Bush initiative requires the United States to withdraw from the U.S.Russian Anti-Ballistic Missile (ABM) treaty, which Tokyo has long regarded as an important element of strategic stability. An integrated U.S.-Japan BMD capability aimed at protecting third countries would raise the same constitutional issues. Japan has not made a decision regarding the acquisition of a missile defense capability. Japanese policymakers and defense firms generally are enthusiastic about missile defense cooperation, but the political parties, the media, and the general public are split over the issue. Proponents view BMD cooperation as a means to counter a perceived North Korean missile threat, and perhaps a Chinese threat as well. Other Japanese are fearful of aggravating relations with China or triggering an Asian missile race. Even groups in Japan favoring BMD cooperation are concerned about the large costs associated with the still-unproven technology. The popular Koizumi administration seems inclined to finesse the constitutional issue, if possible. Japan's future stance will likely depend on regional developments and how the issue plays out in the currently unstable political environment.