The aim of this thesis is to propose a comprehensive national legal framework for the effective and reasonable exercise of universal jurisdiction, which allows states to fulfill their international obligations to prosecute and punish the gravest human rights violations, while respecting other states' sovereignty and preserving the rights of each individual to a fair criminal prosecution and trial. The study is structured in three parts. Part I covers universal jurisdiction in international law. It responds to the question of what states are allowed – and/or obliged – to do under international law. Part II focuses on national legislation to identify if the universality principle is provided for and under what conditions. Our analysis of state legislation and practice has led to the identification of four potential preconditions to the assertion of universal criminal jurisdiction, which are developed in Part III, the main part of the thesis.