Proliferation of armed groups poses a challenge to the framework of international humanitarian law. Are the existing mechanisms under IHL sufficient to ensure compliance with the law by such groups? The purpose of this thesis is to examine how socialisation, by which I mean a process of internalising a norm or a rule, might contribute to producing long-term rule-consistent behaviour. I begin with identification of the legal framework applicable to internal conflicts and challenges associated its practical implementation. Following is the discussion of the ideas on socialisation and their utility in the context of IHL and armed groups. I then proceed to present a particular example of positive engagement with such groups under the so-called Deed of Commitment, launched by a Swiss NGO, Geneva Call. In the final chapter, I return to my analytical framework, apply it to the system established under the Deed of Commitment, and assess to what extent socialisation and positive engagement may ensure greater respect for humanitarian rules. I conclude that socialisation is a valuable tool that may complement existing mechanisms under IHL and, under certain conditions, contribute to long-term rule-consistent behaviour.