Meaning
International Criminal law herein after ICL is a body of public international law that establishes the Individual criminal responsibility for international aims such as war crimes, crimes against humanity, genocide, aggression etc.

It is normally understood as an act that violates fundamental interests of international community and entails individual criminal responsibility.

The current system of ICL works through adhoc tribunals, hybrid tribunals and international Criminal Court.

Nature
certain times are international in nature. They maybe trans-border crimes or committed in high seas or international airspace.

Nature of icl can be categorized as:

1. Crimes by national governments
   Crimes by national government or by individuals who directly control them are at the core of international Criminal law. The victims of such crimes are nationals of other states (civilians) but often they are citizens of criminal states. Here ICL overlaps with human rights law.
    
2. The first modern international Criminal tribunal was held in Nuremberg, Germany in 1945-1946.
   
   This tribunal tried three types of offenses:
   
   1. Crimes against peace
   2. War crimes
   3. Crimes against humanity
    
3. Crimes against peace
   These consist of acts of war and aggression. Although aggression has been defined in the UN General Assembly, the question of how to define individual responsibility to it still remains ambiguous.
   
   The International Criminal Court (ICC) has jurisdiction over crimes of aggression. However, it can't exercise authority until there is agreement both on the definition of aggression suitable for individual criminal precaution and the role of the United Nations Security Council in determining when aggression takes place.

There have been no prosecution for agression and crime against peace since world war 2 trials.

Scope
There are principles of natural law recognised under international law and support atleast some further expansion of scope of ICL.

• Jurisdiction
  It is limited to genocide, crimes against humanity, war crimes, and crimes of aggression. These are settled with a view of the international community at least since Nuremberg, what should be prosecuted internationally. This relative confinement has been criticized by jurists like Cryer, Kress, Heller, and Schmidt. Some international concerns that can be a reasonable expansion of existing crimes:
  1. Environmental degradation (as a crime against humanity)
  2. Cyberwarfare (as aggression)
  3. Mistreatment of migrants (as a crime against humanity)

• Structural limits to expansion
  It is given of the international political order that states are reluctant to formulate legal prohibition that they themselves are likely to fall out of. The evolution of ICL has been slow and in its present form represents a hard-won accomplishment in the name of reluctance (which is still evident in deliberations of the Security Council). The doctrinal limits to expanding jurisdiction concern the conservative nature of legal interpretation. It must reflect the original purpose of the law and not just be bent according to present needs when dealing with criminal law. We demand clarity and prospective criminalization and adjudication as radical change in law can be injustice.

• Expanding jurisdiction
  This gives a principled but curbed grounds for the expansion of ICL in the face of institutional and political barriers. If ICC, just like ICJ, was able to give an advisory opinion, we would be able to transcend at least some more conservative doctrinal limits on ICL while not directly engaging in the prosecution of individuals.