The nominally "teen-age" science-fiction novels of Robert A. Heinlein stand so far apart from even their best competitors as to deserve a separate classification. These are no easy, adventurous, first-steps-to-space boys' books, but mature and complex novels, far above the level of most adult science fiction both in characterization and in scientific thought. Time for the Stars … is one of the best—and possibly the most difficult for the novice. This story of the first exploration outside the solar system combines humor and adventure with pretty intensive speculation on the mathematics and philosophy of time and relativity, the unused reaches of the human mind, and even a skilful touch of psychoanalysis. This may be too meaty for some young readers; but those who have relished the other Heinlein novels (and how adroitly he has brought his readers along from the relative simplicity of "Space Cadet"!) should find it stimulating.