When national security professionals discuss "missile defense" they are are typically referring to technologies that can intercept an in-coming nuclear missile and blow it out of the sky.

In 2002, the George W. Bush administration unilaterally withdrew from the Anti-Ballistic Missile Treaty the US signed with the Soviet Union in 1972. Since then, there has been a sharp increase in the development of missile defense technologies around the world. This has seriously complicated nuclear deterrence 

Sanne Verschuren is a Stanton Nuclear Security post doctoral fellow at the Center for International Security and Cooperation at Stanford University. She is working on a book about why missile defense developed and takes the forms that it does today. The book is built from her dissertation on the topic, which was awarded the prestigious the Kenneth Waltz Award for Outstanding Dissertation in the field of International Security Studies.