Experts on mission may be retained by way of a contract known as a consultant contract, which sets out the terms of their appointment and the tasks that they must discharge. Other individuals may have the status of experts on mission, even though they do not sign a consultant contract, if they are designated by United Nations organs to carry out missions or functions for the United Nations (for example, rapporteurs of the Commission on Human Rights, rapporteurs and members of its Subcommission on the Promotion and Protection of Human Rights and members of the International Law Commission).

For more detailed provisions please refer to the administrative issuances related to this topic.