The idea behind a world citizenship is that a person’s identity transcends geography or political borders and that the own responsibilities or rights are derived from membership in a broader class, named “humanity”.

This does not mean that such a world citizen or cosmopolitan denounces or waives the own nationality or other, more local identities, but such identities are given “second place” to the membership in the world community. 

Here you find supporters for the idea of one world and a world citizenship.