This chapter evaluates legal texts, State practice, and opinio juris to assess how the Syrian conflict both reflected and affected R2P’s development, interpretation, and application. In addition to engaging with some of the more prominent debates on R2P’s application in Syria (most particularly, regarding the employment of the veto and the consequences of non-intervention), it also explores other aspects pertaining to the doctrine’s invocation, including the use of third-party countermeasures by the League of Arab States (in the form of economic sanctions, asset freezes, a civil aviation ban, and the suspension of Syria from its seat); the international reaction towards chemical weapons use and how this reconciles with R2P; the relationship between R2P and humanitarian access, as well as how such access could have been ensured in the Syrian case; the pursuit of accountability outside the purview of the UN Security Council for perpetrators of international crimes in Syria; the applicability of R2P to non-State actors; and the role that R2P could have or should have played in the US-led coalition’s intervention against the Islamic State and Al-Nusra Front terrorist groups in Syria. The chapter concludes with the extrapolation of general conclusions regarding R2P’s applicability, strengths, weaknesses, acceptance by States, and future invocation, bearing in mind the lessons of the Syrian conflict.