This chapter examines the literature surrounding insurance strength ratings. We first describe the general insurance rating landscape for US-based insurers. We then review the rating literature which examines the “quality” of insurer financial strength ratings. We then provide a thorough summary of the existing literature studying the determinants of the insurer financial strength ratings. However, we do not attempt to examine every study that includes a rating variable. Rather we show that insurer financial strength ratings do convey important information to decision-makers as well as the current knowledge about the composition of the ratings. Understanding these components is sufficient to understand the ubiquity of the inclusion of ratings into academic studies of insurers.