P.T. Gilliam's Guide to Sentient Species is a reference work by P.T. Gilliam which gives illustrations and blurbs of information about several sentient species. The book has gone through four editions, each adding several species that were previously not included. As is inevitable in any paper-based tome, however, it's still missing more than 99.9% of them. This is only a big deal if the species you can't find in it is about to endanger you.