For more than four decades, the US has devoted substantial resources to developing antiballistic‐missile systems. During most of that period, effort was focused on developing systems that would defend against the thousands of intercontinental ballistic missiles (ICBMs) fielded by the Soviet Union. Recently, attention has shifted to systems that could counter ICBMs that North Korea or Iran might deploy. Although neither country currently has ICBMs, the US intelligence community projects that they are likely to develop or acquire them within 10 to 15 years.