The first ever Illustrated Checklist of the Birds of the World is really two works in one. It is a complete checklist whose taxonomy incorporates the most up-to-date information and an exhaustive methodology (Tobias et al. 2010) in an entirely systematic and consistent way. At the same time, it contains illustrations and distribution maps for every bird species in the world. This includes the original artwork from the HBW series, as well as hundreds of new illustrations, all in two compact volumes (Volume 1: Non-passerines & Volume 2: Passerines).
An extensive introduction, with many illustrated examples, explains the rationale and advantages of the taxonomic system adopted in the Checklist, as well as how to use the book. With the guidance of many genetic studies and the aid of the scoring system employed to evaluate differences in morphology, vocalizations, ecology and geographical relationships, the number of taxonomic changes for the passerines has been significantly high. At present (totals may change slightly before publication), the volume 2 has 41 lumps and 628 splits, compared with the taxonomy presented in the HBW series.
Large-format maps offer the reader assistance in interpreting the distribution sections. They provide both administrative and physical details, for greater clarity of use.
In total, Volume 2 deals with 1 order, 138 families, 1,358 genera, 6,592 extant species, 57 extinct species, and has 2809 bibliographical references.