The diversity of all turtles and tortoises (chelonians) in the world that has existed in modern times (since 1500 AD), and currently generally recognized as distinct by specialists in turtle taxonomy and systematics, consists of approximately 330 species, of which 57 are polytypic, with 125 additional recognized subspecies, or 455 total taxa of modern chelonians. Of these, 8 species plus 2 subspecies, or 10 total taxa, of tortoises and freshwater turtles have become extinct since 1500 AD (see Table 1), leaving us currently with 322 species and 123 additional subspecies, aBsTracT.-This is our fifth annual compilation of an annotated checklist of all recognized and named taxa of the world's modern chelonian fauna, documenting recent changes and controversies in nomenclature, and including all primary synonyms, updated from our previous four checklists (Turtle Taxonomy Working Group 2007b, 2009, 2010; Rhodin et al. 2008). We continue to provide an updated comprehensive listing of important aspects of taxonomy, names, distribution, and conservation status of all turtles and tortoises of the world. We strive to record the most recent justified taxonomic assignment of terminal taxa in a hierarchical framework, providing annotations, including alternative possible arrangements, for some recently proposed changes. We provide common English names and detailed distributional data for all taxa, listing occurrence by countries and many smaller political or geographic subunits (states or regions), including indications of native, extirpated, and introduced (modern or prehistoric) populations. We also include current published and draft IUCN Red List status determinations for all turtles, as well as CITES listings. The diversity of turtles and tortoises in the world that has existed in modern times (since 1500 AD), and currently generally recognized as distinct and included on this checklist, now consists of 330 species. Of these, 57 are polytypic, representing 125 additional recognized subspecies, or 455 total taxa of modern turtles and tortoises. Of these, 8 species and 2 subspecies, or 10 taxa, are extinct. As of the current IUCN 2011 Red List, 134 turtle species (58.8% of 228 species listed, 40.6% of all species) are officially regarded as globally Threatened (Critically Endangered, Endangered, or Vulnerable). We now record additional draft Red List evaluations of the 102 previously "unevaluated" species, and updated draft re-evaluations of previously listed species, allowing us to evaluate the overall current threat levels for all turtles and tortoises. Of the 330 total species of turtles and tortoises, 149 (45.2%) are Threatened, with 98 (29.7%) Critically Endangered or Endangered. If we adjust for predicted threat rates of Data Deficient species, then 52% of all turtles are Threatened. If we include Extinct in the Wild and Extinct species, then 48.0% of all modern turtles and tortoises are recorded as either already extinct or threatened with extinction, with a predicted rate of 55% threatened and extinct. Turtles are a...