The adoption of thematic resolutions by the Security Council in the last 15 years enhanced existing and developed new legal regimes. This is a shift both in international law, traditionally adopted by states through treaties and conventions, and in the Security Council’s approach to international peace and security, oriented originally on determining and addressing only country-specific threats. The Security Council has traditionally acted as a global ‘executive’ and as a ‘quasi-judge’, investigating and defining threats and imposing sanctions on states, threatening the peace. The new practice of thematic resolutions developed a third role of the Council – as a global ‘legislator’ – addressing generic and non-country-specific threats – such as terrorism, proliferation of weapons of mass destruction, targeting of civilians, recruitment of child soldiers, piracy, HIV/AIDS etc. – and urging States to adopt measures to combat those threats. Some of the legislative resolutions have been enforced through special implementation mechanisms, such as sanctions committees or additional Chapter VII measures, making them more robust than the regimes established by international treaties. Although some research and publications on various thematic resolutions – mostly on anti-terrorism, protection of civilians, international criminal justice – have been undertaken, this project – reflecting on this literature – offers a more holistic assessment of international legal regimes affected by the Security Council surge in thematic resolutions. The novelty is also in the attempt to situate and discuss the legislative role of the Council (in addition to its executive and quasi-judicial roles) making comparisons with the roles similarly played by the three branches of power (legislative, executive, judicial) in domestic systems and how does this activity of the Security Council challenges and develops the international constitutionalism.