‘Leave No one Behind: The Role of Freedom of Religion or Belief in Advancing Human Flourishing and Just Societies was the theme of the Fourth International Parliamentarians Conference on Freedom of Religion and Belief (FoRB) held in Nairobi, Kenya, from 1-4 May 2023. The Nairobi Declaration is a document signed by Parliamentarians worldwide at the 4th International Parliamentarians Conference on Freedom of Religion and Belief (FoRB).