In this paper I discuss a number of different relationships between two kinds of (moral) obligation: those which have individuals as their subject, and those which have groups of individuals as their subject. I use the name collective obligations to refer to obligations of the second sort. I argue that there are collective obligations, in this sense; that such obligations can give rise to and explain obligations which fall on individuals; that because of these facts collective obligations are not simply reducible to individual obligations; and that collective obligations supervene on individual obligations, without being reducible to them. The sort of supervenience I have in mind here is what is sometimes called ‘global supervenience’. In other words, there cannot be two worlds which differ in respect of the collective obligations which exist in them without also differing in respect of the individual obligations which exist in them.