This book is one of my favorites of the year, and I would imagine it's one that the Caldecott committee will discuss at length. (It has also recently been named a NYT Best Illustrated book.) Mac Barnett's excellent storytelling, combined with Christian Robinson's illustrations, make this a true picture book. Robinson's childlike illustrations (a mix of acrylic paint and paper collage) may look effortless and simple, but a close look reveals the details and intentionality in each spread. Take, for instance, Leo the invisible ghost. Robinson makes sure readers see him by outlining him in blue while keeping most of his figure transparent. Leo's soft blue outline contrasts with the sharper angles of most of the humans he encounters, except of course, for Jane (who is shaped very much like Leo, if more solid).

One particular Caldecott criterion in identifying a "distinguished American picture book" stands out when looking at Leo: "Delineation of plot, theme, characters, setting, mood or information through the pictures." Barnett's straightforward text leaves so much room for the illustrations to tell the story. The color palette lends a vintage feel that fits a ghost story and establishes a more subdued tone. And right from the beginning, the illustrations fill in the gaps: on the first page we read that Leo is invisible, but on the next, readers can see him — although some kindergarteners will tell you that they see him on the first page, too.

The book's design enhances and furthers the story. A partially visible Leo next to the door on the title page is completed at the end of the book on the page opposite the copyright information (on the title page he is walking through a wall; opposite the copyright information, he walks through it to the other side). Robinson utilizes spot illustrations as well as single- and double-page spreads to great effect; the double-page spread where Leo leaves his home to roam is especially effective. The long road's perspective leading away from the house epitomizes Leo’s loneliness and indicates a potentially long journey. The text placement, different on every page, takes illustrations and word flow into account, drawing readers' eyes so that they take in the story in its entirety. And for picture book (and knights of the Round Table) enthusiasts, Leo's coat of arms hidden underneath the book jacket is pure gold.

Barnett and Robinson's collaboration is one of the most unusual and charming books I’ve come across this year. And while child appeal may not explicitly be part of the Caldecott criteria, the fact that this book is a fast favorite for so many young people certainly adds to its merit.