It contains Barlowe's visualizations of different extraterrestrial life forms from various works of science fiction, with information on their planetary location or range, biology, and behaviors, in the style of a real field guide for animals.

The book contains descriptions of the following species: Barlowe's Guide to Extraterrestrials received a mixed review from Wendy Bousfield in Library Journal.

Bousfield commented that the book's drawings were "colorful", but also "somewhat static and artificial-looking, with less vitality than the preparatory sketches from the artist's notebook included at the end."

[3] The book received a positive review from Claudia J. Morner in School Library Journal.

She concluded that it was a "fun browsing book" that would appeal to "young people fascinated by monsters" as well as to science fiction readers.