The assessment of military conduct during armed hostilities as either lawful or criminal involves striking a balance between the requirements of humanity and those of military necessity. Throughout its existence, the International Criminal Tribunal for the former Yugoslavia (ICTY) has tackled this balancing exercise in the context of individual criminal responsibility by reference to the laws of war. Indeed, the Appeals Chamber of the ICTY in the Kunarac case noted that “the laws of war provide a benchmark against which the Chamber may assess the nature of the attack and the legality of acts committed in its midst”. Accordingly, for many years, the Trial and Appeals Chambers of the ICTY have been guided by the well known principles of distinction and protection, which, according to one of the Trial Chambers, form “the foundation of international humanitarian law”. In applying these guiding principles the Chambers have also had regard to and analysed the prohibition against indiscriminate and disproportionate attacks. This has all been done in the context of the Statute establishing the ICTY. The relevant provisions in the Statute are Article 2 (grave breaches of the Geneva Conventions), Article 3 (violations of law or customs of war other than those covered by Articles 2, 4, and 5), and Article 5 (crimes against humanity). This paper considers pertinent ICTY’s jurisprudence and provides an overview of the application of these principles in the various cases. In doing so, it focuses on those most relevant to the issue of what qualifies as lawful conduct in armed hostilities.