This is the famed Peterson's Guide. It is illustrated using paintings by Roger Tory Peterson. In a nice touch, the incomplete plate (page with the painting of birds) that he was working on when he died is found in the preface by his wife, and the forward references the completed version that was completed by a friend for inclusion in this Fifth edition.
The plates include lines that indicate field marks. The actual mark descriptions are in the short paragraph that is with each bird. Between 4 and 6 birds are in every pair of facing pages, with between 1 and 5 poses for each bird. The illustrations are fairly large, and clear. The text covers several categories, visual description included differences between male, female and juvenile, similar species, description of the range, voice, and habitat. With this much to cover, the wording is terse.
Also, there is a thumbnail range map. A larger range map is in the back. There are many reviewers who complain about the range maps being in the back of the book, presumably they are discussing a previous edition.
What Peterson introduced with this guide was a way to identify species in the field, without having to capture or shoot the specimen. In this case, the field marks. For each species, he gives marks (distinctive markings) that distinguish one bird from others of the same family. For example, if a woodpecker is small and has a red spot on the nape of the neck with a white stripe down the back, it could be Downy woodpecker. But if its bill is as long as its head and the outside tail feathers are all white (no black spots) it probably is a hairy woodpecker. If it is large, has a red crest that extends to its bill, and the wing has a white leading edge and black trailing edge, it is a Pileated. If the trailing edge is white, the red crest does not go all the way to the front of the head and you are in a southern old growth forest, well, that could very well mean something else, especially in 2005-2006.
I suppose that a true birder does not memorize field marks, instead has an intuitive understanding just by looking as to what species a given bird is. But for those of us who have not attained enlightment, we identify the basic type, then use the marks to home in on the species, or note things to look for when we hit our field guide. And the Peterson's does a good job of that.
For identiying what is in the air around us, this is a delight to use, and the order gets intuitive after not long. There is something thrilling of paging through a field guide and realizing you just figured out what that bird you could not identify was, and going out in the field again and wondering if you will see it again.
This is a field guide, and its purpose is identification. It is not a guide of ornithology. If the goal is to understand birds, look elsewhere. But it serves its purpose well, and its cover and construction give me confidence it should survive many walks stuffed in my jacket pocket and thumbed through in the field.