This chapter focuses on the relationship between the state, attitudes to warfare as enshrined in Christian theory, and the practice of warfare as exemplified in medieval eastern Roman, or Byzantine, relations with its various enemies, with a short introductory section on violence in non-warfare contexts. While nominally opposed to violent means to achieve its ends, the Christian Byzantine state found ways to justify engaging in warfare against its enemies, primarily based on the notion that it was involved in a perpetual defensive struggle with those who threatened its territorial integrity as well as its moral existence. All warfare could thus be understood by definition as a defensive struggle against those who threatened the empire’s existence. This applied likewise to overtly offensive warfare, which was legitimated within a Christian eschatology as a divinely-approved effort to recover lost territories and restore them to the Christian community. Hence, no theory of ‘holy war’ or ‘crusade’ evolved, because such was irrelevant. Such an ideology offered a constant theoretical basis for fighting the empire’s foes; and it also served the needs of the imperial elite and the court on an opportunistic basis, to justify offensive warfare whenever the empire was in a position to undertake such action. Such an ideology legitimating warfare could also deployed against Christian neighbours, when it suited the interests of the imperial state or its elite.