How does international law apply in a domestic legal system?

Dualist and Monist Systems

States see the interaction between international and national law in two different ways. Monism and dualism are used to describe these two different legal traditions.


In States with a monist system international law does not need to be translated into national law. The act of ratifying an international treaty immediately incorporates that international law into national law. The ICC Statute, therefore, can be directly applied and adjudicated in national courts.

“Monist systems” do differ in  their approach.

  • Under some Constitutions direct incorporation of international obligations into the domestic law occur on ratification.
  • In other States direct incorporation occurs only for self-executing treaties.


For States with a “dualist system”, international law is not directly applicable domestically. It must first be translated into national legislation before it can be applied by the national courts.

Therefore, for a dualist State ratification of the ICC Statute is not enough and national implementing legislation is necessary. War crimes trials, for example, can only take place when the national legislation is enacted, unless of course such legislation already exists.

Example: Holland – a monist system, with implementing legislation

New national provisions for crimes against humanity, laws on cooperation and transfer of suspects.

The Netherlands signed the Rome Statute on 18 July 1998 and ratified it on 17 July 2001. Despite being a monist system, the view of the Netherlands is that as a State Party it is obliged to implement the Statute through national legislation.

The International Criminal Court (Implementation) Act and the accompanying Amendment Act were both enacted on 20 June 2002. The Implementation Act entered into force on 1 July 2002, giving the Dutch Government a statutory basis for transferring suspects to the ICC and for cooperating with the ICC.

War crimes and genocide have for many years been defined as criminal offences under Dutch law. Therefore persons accused of these crimes could stand trial in the Netherlands even prior to the ICC Statute coming into force. To make it possible to try persons accused of crimes against humanity, however, the Netherlands needed to translate the relevant ICC Statute provisions into national law. The International Crimes Act was enacted on 19 June 2003 and entered into force on 1 October 2003. This brought Dutch criminal law into line with the ICC Statute’s requirements, and engaged the principle of complementarity.