In recent years, supervenience has been the subject of extensive philosophical analysis. Varieties of supervenience have been distinguished, their pairwise logical relationships examined, and their usefulness for various purposes scrutinized. However, despite extensive analysis, some details are askew, some controversies unresolved. I will by no means attempt to straighten out all the details or to settle all the controversies. But I will take a detailed look at what others have said and add a couple of wrinkles.

In Section 1, I present and explore the core intuitive idea of supervenience. In Section 2, I argue that the possible-world versions of weak and strong supervenience do not imply, respectively, the modal-operator versions of weak and strong. In Section 3, I discuss an aspect of global supervenience, in particular what it is for two worlds to have the same total pattern of distribution of properties of a certain sort. In Section 4, I examine the logical relationships between weak and global supervenience, and between strong and global. In Section 5, I make some observations about multiple-domain weak and strong supervenience. In Section 6, I consider whether any variety of supervenience implies reduction. Finally, in Section 7, I briefly note two theoretical uses of supervenience.