The rise of the 21st Century Islamic extremist movement, which was mobilised by the al-Qaeda attacks of and responses to September 11, 2001, heralds a new period in the history of terrorism. The increased frequency and intensity of this type of terrorism affects every nation in the world, not least Australia. Rising to meet the challenges posed by terrorism is the field of terrorism studies, the field which aims at understanding, explaining, and countering terrorism. Despite the importance of the field, it has been beleaguered with criticisms since its inception as a response to the rise of international terrorism. These criticisms specifically aim at the field's lack of objectivity, abstraction, levels of research, and levels of analysis. These criticisms were the impetus behind the adoption of the methodology of this thesis, which offers the distinct ability to understand, explain, and forecast the way in which terrorists interact within covert cells. Through social network analysis, this thesis examines four terrorist cells that have operated in or against Australia. These cells are from the groups Hrvatsko Revolucionarno Bratstvo (Croatian Revolutionary Brotherhood), Aum Shinrikyo (Supreme Truth), Lashkar-e-Taiba (Army of the Pure), and Jemaah Islamiyah (Islamic Community) and operated between 1963 and 2003. Essentially, this methodology attempts to discover, map, and analyse the interaction within the cells during the covert stage of their respective operations. Following this, the results are analysed through the traditional social network analysis frameworks to discover the internal dynamics of the cell and identify the critical nodes (leaders) within the cells. Destabilisation techniques are subsequently employed, targeting these critical nodes to establish the most effective disruption techniques from a counter-terrorism point of view. The major findings of this thesis are: (1) that cells with a focus on efficiency rather than covertness were more successful in completing their objectives (contrary to popular belief); and (2) betweenness centrality (control over the flow of communication) is a critical factor in identifying leaders within terrorist cells. The analysis also offered significant insight into how a Jemaah Islamiyah cell might operate effectively in Australia, as well as the importance of local contacts to terrorist operations and the significance of international counter-terrorism cooperation and coordination.