A number of distinctions are needed to assess The Identity of Indiscernibles. The first concerns its purported status as true or, more strongly, necessarily true. The second concerns the nature of the properties the principle ranges over. One way to divide up properties is in terms of those that entail the existence of a particular object, those that entail the existence of an object but no particular object, and those that don't entail the existence of an object at all. A second way is divide up properties is in terms of ‘indicative’ and ‘counterfactual’ properties. Combining these three distinctions yields twelve different versions of the Identity of Indiscernibles. In the long run, however, four more are needed to do the principle justice. Sixteen different versions of the principle, then, need to be, and in this paper are, assessed. Particular attention is paid to methodology and to constraints on the generation of properties needed to support various versions of the principle. Bottom-up reasoning is found sufficient to vindicate the great majority of them, but there does not appear to be a good bottom-up or top-down argument for the two most interesting and important versions of the Identity of Indiscernibles, and there is some reason to think both false. An open mind needs to be kept, however, for definitively establishing or refuting them probably requires a relatively complete and plausible metaphysics.