This chapter lays down the foundations for the argument that questions of (non-)performance raised by the practical phenomenon of sharing international obligations can be tackled by a further categorization and systematization of international obligations, since different types of shared obligations can have different legal implications. It starts by introducing the distinction between indivisible and divisible shared obligations, after which the analysis turns to the issue of how to ascertain the nature of shared obligations, as it will not always be apparent at first glance whether a particular shared obligation is to be qualified as indivisible or divisible. It will be discussed how the distinction between positive and negative obligations as well as the distinction between obligations of conduct and result can facilitate the categorization of a particular shared obligation as either divisible or indivisible. The chapter ends with some reflections on the performance of shared obligations, highlighting how both indivisible and divisible shared obligations can have relevant implications for what is expected of duty-bearers (though in different ways), necessitating a more collective approach to performance.