International criminal law represents a paradigm shift in legal accountability: it pierces the veil of state sovereignty to hold individuals personally and criminally responsible for the gravest violations of human dignity. Unlike traditional domestic criminal law, which operates within territorial and jurisdictional boundaries, international criminal law recognizes that certain atrocities—genocide, crimes against humanity, war crimes, and aggression—are offences against humanity itself and cannot be shielded by claims of official immunity or state authority. India's constitutional and legislative framework acknowledges this principle through ratification of international conventions and treaties, though the Indian Penal Code and Indian legal procedures remain the primary mechanism through which India prosecutes such offences domestically. The International Criminal Court, established by the Rome Statute, serves as a court of last resort when national courts are genuinely unable or unwilling to prosecute; this subsidiarity principle is foundational—it does not replace national jurisdiction but supplements it. India, though not a signatory to the Rome Statute, remains bound by customary international law and UN obligations to prevent and punish atrocity crimes. The significance for CLAT aspirants lies in understanding that international criminal responsibility is individual, not collective; it attaches to natural persons, not states, and requires proof of mental culpability alongside actus reus. The framework protects even those acting in official capacity—heads of state, military commanders, and bureaucrats—from invoking immunity as a complete defence, though procedural immunity may apply temporarily during office. This represents a fundamental break from classical notions of absolute sovereign immunity and reflects post-World War II consensus that certain human rights violations transcend state borders and demand universal accountability. The four categories of international crimes each carry distinct elements: genocide requires specific intent to destroy a group; crimes against humanity require systematic or widespread attack on civilians; war crimes require nexus to armed conflict and violation of humanitarian law; and aggression requires willful initiation of conflict by state leadership. The International Criminal Court exercises complementarity jurisdiction—it defers to national prosecutions and intervenes only when states manifest unwillingness (through sham trials or immunities) or inability (through state collapse or destruction of judicial capacity) to genuinely investigate and prosecute. For Indian students, the practical application arises when Indian nationals commit atrocity crimes abroad, or when foreign nationals commit such crimes within Indian territory; India's obligation is to investigate and prosecute under domestic law or extradite to the International Criminal Court or other legitimate tribunals. Defences in international criminal law are narrowly construed: necessity, duress, and superior orders do not eliminate responsibility but may mitigate sentencing; the Nuremberg principles, incorporated into customary international law, reject the 'mere instrument' doctrine that held underlings blameless for following orders. The interaction between international criminal law and Indian domestic law creates a jurisdictional interplay—India may prosecute under its penal legislation, treaty obligations, and international customary law principles; however, Indian courts have historically been reluctant to apply extraterritorial jurisdiction without explicit statutory authorization. The broader positioning within international law reveals that criminal responsibility operates alongside civil reparations (compensation to victims), truth commissions, and conditional amnesty, though the latter two cannot entirely displace accountability for the gravest crimes. Neighbouring concepts include crimes against peace (prosecuted at Nuremberg), universal jurisdiction (allowing any state to prosecute certain crimes regardless of location or nationality), and the doctrine of command responsibility, which holds military and civilian leaders liable for subordinates' crimes through failure to prevent or punish. Understanding the interaction between consent (whether a state consents to International Criminal Court jurisdiction), immunity (what procedural shields exist during trial), and complementarity (which tribunal has primacy) is essential for nuanced application.