On 11 June 1998, India announced and confirmed it had carried out a series of underground nuclear tests at the Pokhran test range in the Thar Desert of Rajasthan. The tests, conducted by the Defence Research and Development Organisation and overseen by India’s civilian and military leadership, comprised multiple detonations intended to demonstrate both fission and thermonuclear capabilities. The Indian government framed the tests as necessary for national security and technological sovereignty after decades of nuclear development. The detonations ended a long period of strategic ambiguity. India had previously conducted a “peaceful nuclear explosion” in 1974, but the June 1998 tests were explicitly portrayed by New Delhi as weapon-related, with officials declaring that India now possessed nuclear deterrent capability. The tests occurred in a regional context of rivalry with Pakistan, which quickly responded with its own series of nuclear tests later that month, escalating tensions on the subcontinent and spurring a regional arms dynamic. International reaction was swift and largely critical. Major Western countries, including the United States, imposed economic sanctions and suspended certain forms of bilateral cooperation. The tests were condemned as contrary to global non-proliferation norms; governments and international organizations called for restraint, diplomacy, and a return to arms-control frameworks. Several countries also reassessed their strategic relationships in South Asia and sought to reduce the immediate risk of military escalation between India and Pakistan. Within India the tests produced mixed domestic reactions. Many political leaders and a broad segment of the public greeted the tests with nationalist pride and saw them as rectifying perceived strategic vulnerabilities. Other voices—among civil society, academics, and political opposition—warned about the economic and diplomatic costs of testing, including sanctions, international isolation, and the risks of an arms race in South Asia. Technically, the June 1998 tests sought to validate warhead designs, delivery compatibility, and yield estimates. Independent seismological monitoring by multiple international agencies detected seismic signals consistent with underground explosions; analyses of those data offered varying yield estimates and led to debate among experts about the number and yields of devices tested. Because the tests were underground and conducted by a sovereign state, some technical details have remained classified or subject to differing assessments. The tests had enduring policy consequences. They prompted renewed international attention to non-proliferation regimes, including the Nuclear Non-Proliferation Treaty (NPT) and export control regimes. Diplomatic efforts intensified to reduce tensions in South Asia, culminating in confidence-building measures between India and Pakistan in subsequent years, though mistrust persisted. Over time, India pursued formal and informal strategic partnerships with select countries while also seeking recognition of its status as a responsible nuclear power—an effort that included negotiations leading to agreements on civilian nuclear cooperation with several states in the following decade. Scholars and policymakers continue to debate the long-term strategic effects of the 1998 tests: whether they enhanced Indian security through deterrence, accelerated a regional arms competition, or both. What is clear is that the events of June 1998 marked a pivotal moment in South Asian security dynamics and in global non-proliferation discourse, with ramifications that have shaped regional diplomacy and nuclear policy ever since.