The chapter explores the doctrinal and political debate concerning the compatibility of the different forms of support that Italy provided to Ukraine following the Russian invasion of 2022 with the “pacifist clause” enshrined in article 11 of the Italian Constitution. The chapter highlights how the war in Ukraine revealed a sharp contrast between “radical pacifist” interpretations of article 11, according to which Italy should have remained perfectly neutral in the conflict, and “internationalist” interpretations of the same clause, according to which the right to use war as an instrument of self-defence shall allow Italy to provide help to other States (and peoples) facing an unjust war of invasion. A special focus will be dedicated to the possibility of inferring an ontologically autonomous definition of “peace” and “illegal war” directly from the Constitution and without deferring exclusively to the rules of international law.