In an exchange of letters, James Lindsay and Michael O’Hanlon claim that in arguing that the costs of a national missile defense outweigh the benefits, the authors underestimate or ignore three possible scenarios that support the development of a limited NMD system. The authors respond.

As the debate on a U.S. national missile defense intensifies, the decision about whether the United States should develop an NMD system seems to be giving way to questions over the type of system to be deployed and its scope: For example, should the United States pursue NMD against Russia or China? What are the possible security benefits and costs of limited NMD? What can the United States do to counter the international political fallout of limited NMD?

The usefulness of offense-defense theory is the subject of our correspondence section.

The authors respond to two major criticisms of offense-defense theory: first, that the theory lacks a commonly accepted definition of its key independent variable—the offense-defense balance—and, second, that the offense-defense balance cannot be measured.

Current U.S. nuclear strategy identifies new nuclear counterforce missions as a means of impeding the proliferation of weapons of mass destruction.

This article offers a new perspective for assessing the consequences of arms buildups by posing a different question: Is an arms buildup the best way for a state to achieve security and to protect other vital interests?