Yousif's areas of research interest are public international law, international criminal law, and international human rights law. In particular, his areas of expertise include the doctrines of immunity, norms jus cogens, and universal jurisdiction.
He is also interested in applying the test of legitimacy, specifically coherency/integrity, to measure the effectiveness and efficiency of rules in the international legal system.
Other areas of interest include problems arising from disputes amongst international bodies. In particular, the African Union, International Criminal Court, and the United Nations.