This thesis examines conceptualisations and representations of war in International Relations theory using the NATO intervention in Kosovo. By examining this historically important case, I clarify the process by which theoretical conceptualisations present phenomena and the critical themes needed to analyse complex phenomena. I examine the dual process of conceptualisation and representation evident in the phenomenon of war presented in International Relations theory. I use two major research strategies; first, a critical analysis of the representations and conceptualisations of phenomenon, and secondly, qualitative analyses of a case study. Data has been collected from the internet, archives, political statements, interviews, newspapers, television sources, theoretical papers and published reports. There is considerable variation across the two arenas of representations and conceptualisation evident in the practical and theoretical inconsistencies when re-visiting the case study. Typically theoretical abstractions dis-engage with alternative representations, the literature of war, and a variety of forces such as the psychological dynamics at play in war, which provide two examples of the sites needed to conceptualise such complex phenomena. Nevertheless, theoretical conceptualisations have gained credence and acceptability in the discipline of International Relations without examining the impact of wider social and discursive representations. Using a range of source material demonstrates how a prior theoretical process overcomes the interaction between representations and conceptualisations of phenomena. As a result, the thesis also demonstrates how the reconceptualisation of phenomenon has had a substantial impact on the formation of critical theory in International Relations. In some cases, critical readings converge to form a more effective interpretation of both phenomena and conceptualisations. However, the degree of influence within alternative representative sites has declined over time. This thesis challenges the argument that effective interpretations of the phenomena of war exist in International Relations theory and instead the thesis takes the view that multiple representations of war are needed to engage with such complex phenomena. In order to demonstrate this, the thesis develops an original methodological style based on a synthesis of critical approaches. At the same time, the thesis is original because of theoretical depth of the analysis undertaken here and also in the way the research positions itself against the conventional literature. Therefore, the research undertaken in this thesis is grounded in evidence from a case study and is examined using an original methodological approach in order to develop a more effective reading of the phenomenon of war.