The idea of global justice is comparatively new: it was rarely used before the last decades of the twentieth century. The idea of social justice, by contrast, has been with us for a century or more. When a new political idea appears in the wake of a longer-established one, it is natural, perhaps almost unavoidable, to see the second as simply a development of the first. Social justice was a central idea in twentieth century politics, in democratic societies especially. It was the banner under which the battle for equal rights, equality of opportunity, the welfare state and other such goals was fought within each separate state. Alongside the political battle, philosophers elaborated numerous theories of social justice, the most celebrated perhaps of which was that of John Rawls, as set out in his book A Theory of Justice and later works. So, when later on these philosophers and others began to think about what justice might mean on a global scale, it was natural that they should start by taking familiar principles of social justice and exploring how these could be applied beyond the realm of domestic politics. The implicit assumption here was that at a fundamental level social justice and global justice are one and the same, the difference between them being essentially a practical difference of scope: social justice is justice within bounded societies, while global justice is justice across humanity as a whole. In line with this, the use of the phrase ‘global social justice’ in popular political discourse makes this assumption evident.