Coordinated Management and Emergency Response Assemblages (CMaERAs) are complex, multi-faceted, institutionalised networks of emergency response agencies, people, processes, technologies, histories, geographies and cultures which shape the strength of inter-agency coordination and emergency response. This thesis explores how a variety of actors, actants and technologies involved in emergency management assemble and organise. The methodology adopted is qualitative and uses two case studies to evaluate how CMaERA oscillate from their organised shape as dictated by policy to a new shape emanating from the needs of a response call. The case studies were: the Irish Emergency Management Assemblages (IEMA) response to the winter storms of 2015/2016 and the United States Emergency Management Assemblages (USEMA) response to the Boston Marathon Bombing in 2013. Fifty-one semi-structured interviews of key stakeholders and emergency response agents were conducted and supported by an interpretive analysis of key policy documents. By adopting assemblage theory and applying it to the empirical findings of the IEMA and USEMA, conceptualised within Foucauldian and Agambien understanding of power and sovereignty, this thesis offers a theoretical and philosophical framework to study emergency services, their interactions and power dynamics while keeping in sight their histories, cultures and current situations. This resulted in recognising that CMaERAs re-shape and oscillate position regularly to ensure that response is adequate and efficient. These movements are influenced both by the situation, inter-agency trust, and previous working relationships, but also from external factors, such as the institutionalisation and siloed manner of agencies, (in)formalisation, their relationship with the government, technological advancements, data analytics but also human nature. These broad factors affect inter-agency coordination and collaboration by creating barriers preventing the development of a true Coordinated Management and Emergency Response Assemblage. Finally, it provides three wider contributions to knowledge: expansion of the term ‘vulnerability’, development of embodied assemblages, and the identification of three urban factors which affect assemblage oscillation.