This chapter gives an overview of the literature on identity-based signature (IBS) schemes, from Shamir's seminal scheme to the current state-of-the-art. Rather than presenting all schemes separately, we present three generic transformations that together cover the majority of known IBS schemes as special cases. The first transformation follows a certification approach based on standard signatures; the second is a transformation in the random oracle model from “convertible” identification schemes; and the third is based on hierarchical identity-based encryption. We also discuss a number of direct schemes that escape being covered by any of the generic transformations. Finally, we show how the principles of the first transformation can be extended to a hierarchical setting and to IBS schemes with special properties.