The Introduction gives an overview of the book’s most important findings and contributions. Since international relations are anarchical and international legal norms are incomplete or in tension with other norms, there is potential for contestation whenever a general norm is applied to specific situations. The reactions of others to proposed norm interpretations can alter norms and their strength. The second section describes the book’s rhetorical approach, and the third section summarizes the main theoretical contributions. First, the "alternate endings" typology shows that it matters whether dispute parties (dis)agree on the norm frame or behavioral claim. Frame agreement is an internal source of stability. Moreover, the typology can guide assessment of how contestation affects norm strength. Second, I describe the focus on audience reactions, argumentation, and speakers (including delegation to agents) when analyzing extrinsic influences on the persistence of norm interpretations, and thus of alternate endings. The fourth section discusses the main contributions to the existing literature on norm strength, the dual quality of norms, legal argumentation and interpretive communities, and delegation to courts and other relevant agents. The Introduction then discusses the research design and methodology, before concluding with an overview of the remaining chapters.