By the mid-1990s when the term, ‘Second Nuclear Age’ started appearing in the writings of analysts, there was a dim realisation that new players would emerge on the nuclear scene. After 9/11, the threat perceptions on account of global terrorism grew, and they have remained a persisting concern. Yet, the international strategic community’s efforts have been focused largely on preserving the existing nuclear order rather than figuring out how it may need to evolve in the so-called Second Nuclear Age. It is clear that today, new semantics is needed—one that reflects the current political dynamics if the nuclear taboo that has existed since 1945 is to be sustained. This monograph addresses this challenge of furthering a discussion on evolving a new vocabulary and grammar for a 21st-century nuclear order. Our contributors include both practitioners who have been engaged in nuclear negotiations, and academics; in some cases, the author straddle both domains. Although the authors differ in terms of how much we can rely on old instruments and maps, there is broad agreement that we are navigating uncharted waters.