The purpose of this thesis to to investigate if the complex and ambiguous means of a hybrid warfare strategy in the context of the ‘armed attack’ threshold. The ‘armed attack’ threshold sits within the UN Charter article 51 and it constitutes the legal provision that the right to self-defence, both unilaterally and collectively, is only triggered in the event of an ‘armed attack’. It is therefore important to determine if this threshold can through the ambiguous and complex structure of hybrid warfare be circumvented or obfuscated to prevent, delay or weaken a State’s ability to act in self- defence or by other means. To examine this problem, this thesis approached it by describing the concept of hybrid warfare and the legal framework that constitute the ‘armed attack’ notion in the context of self-defence. And by, to the extent possible analysed if the hybrid warfare means; cyber warfare, information warfare and the use or support of proxy forces could individually amount to an ‘armed attack’ by viewing how these means were used in Ukraine by Russia. This thesis argues, that a hybrid adversary can through the inherently complex and ambiguous nature of hybrid warfare and its means, obfuscate its attribution under certain circumstance to prevent, limit or delay the ability of a State to act in self-defence or by other means.