Common law countries are those that have a legal system based on judge-made law, rather than codified law. The United Kingdom is a common law country, while France, Germany, and Japan are civil law countries.

The principle of nullum crimen sine lege means that an act cannot be punished as a crime unless it is clearly defined as such in the law.

The definition of crimes can vary significantly from one jurisdiction to another. For example, the definition of murder may include different elements in different jurisdictions, such as the intent to kill or the degree of premeditation.

International law plays a vital role in criminal justice by providing a framework for cooperation between countries, establishing universal jurisdiction over certain crimes, and creating international criminal courts.

Cross-border criminal investigations and prosecutions face a number of challenges, including differences in legal systems and procedures, language barriers, and lack of cooperation between countries.

Cross-border crimes are crimes that involve the movement of people, goods, or money across international borders. Examples of cross-border crimes include drug trafficking, human trafficking, and cybercrime.

The principle of ne bis in idem means that no one shall be tried or punished twice for the same offense.

Crimes against humanity are serious violations of international law that are committed against civilians during armed conflict or other situations of violence. Examples of crimes against humanity include genocide, crimes against peace, and war crimes.

Comparative law plays a vital role in the development of criminal law by identifying best practices, promoting the harmonization of criminal laws, and facilitating the transfer of criminal law knowledge between countries.

Supranational criminal courts are international courts that have jurisdiction over crimes that are committed in more than one country. The International Criminal Court is an example of a supranational criminal court.

The principle of lex loci delicti means that the law of the place where the crime was committed is the law that applies to the crime.

War crimes are serious violations of international law that are committed during armed conflict. Examples of war crimes include murder of civilians, torture, and rape.

Extradition is the process by which one country requests the surrender of a person who is accused or convicted of a crime from another country. It can also be used to transfer a person who is serving a sentence in another country to a prison in their own country.

Crimes against peace are serious violations of international law that are committed against the peace and security of mankind. Examples of crimes against peace include planning, preparation, initiation or waging of a war of aggression, use of force against the territorial integrity or political independence of another state, and genocide.

The principle of territoriality means that a country has jurisdiction over crimes that are committed within its territory, regardless of the nationality of the offender or the victim.