   What sorts of duties of justice, if any, exist among human beings who do not reside in the same country? If there are such duties, what grounds them? Some argue that John Rawls’s principles developed for the case of domestic justice, notably, the Fair Equality of Opportunity Principle or the Difference Principle, should apply globally (Caney 2005, Moellendorf 2002). Others maintain that the content of our duties to one another is best explored by examining alternative concepts not featured in the Rawlsian corpus, such as capabilities or human rights (Nussbaum 2006, Pogge 2008).