This thesis offers a different approach to technology in International Security Studies (ISS). Traditional “grand theories” often treat technology as an “external variable,” a “black box,” or a “deus ex machina,” analysing its impact without sufficiently theorising it as an endogenous factor actively shaped by social and political forces. This limits ISS’s ability to develop a nuanced understanding of the mutual development of technological artefacts and policy frameworks. The thesis proposes and demonstrates the usefulness of applying the Social Construction of Technology (SCOT) approach from Science and Technology Studies (STS) to ISS. SCOT challenges technological determinism, asserting that technology is shaped by human action, social context, and negotiations among “relevant social groups” that define an artefact’s meaning and purpose (interpretive flexibility). By drawing on SCOT concepts such as technological frames and closure, the thesis offers a means to link micro-level technical practices with macro-level international security phenomena. The research, structured as a cumulative dissertation, empirically validates this idea across two key areas within a subfield of ISS: global nuclear governance, specifically nuclear security and non-proliferation. In nuclear security, applying SCOT to nuclear forensics demonstrates how the stabilisation of this discipline resulted from the alignment (closure) of often conflicting technological frames held by scientists, policymakers, and law enforcement, showing that this is a socially constructed outcome rather than purely technical development. Furthermore, analysis of attacks on nuclear installations by states reveals how the technological frames of national nuclear security regimes become vaguely defined during extraordinary circumstances, exposing gaps in governance. In nuclear non-proliferation, the thesis employs SCOT to examine the technical aspects of IAEA safeguards. A key empirical insight is that core technical benchmarks, such as the IAEA’s “significant quantity” (SQ) values (e.g., 8 kg plutonium, 25 kg highly enriched uranium), are not inherent technical truths but are socially constructed outcomes of political negotiation and stakeholder consensus (closure), often derived from documents unrelated to safeguards. The thesis shows SCOT’s policy relevance by arguing that recognising the interpretive flexibility and social construction of technical definitions enables policymakers to move beyond rigid thresholds and adopt more flexible approaches. It underscores the importance of aligning technological frames among diverse stakeholders (e.g., scientists, diplomats, and law enforcement in nuclear forensics) to foster institutional trust and ensure the sustainable operation of international organisations such as the IAEA. By incorporating the SCOT approach, this thesis broadens the conceptual toolkit available to ISS scholars, offering a more detailed understanding of technological agency within the framework of global nuclear governance.