Beginner Books is the Random House imprint for young children ages 3–9, co-founded by Phyllis Cerf with Ted Geisel, more often known as Dr. Seuss, and his wife Helen Palmer Geisel. Their first book was Dr. Seuss's The Cat in the Hat (1957). Cerf compiled a list of 379 words as the basic vocabulary for young readers, along with another twenty slightly harder "emergency" words. No more than 200 words were taken from that list to write The Cat in the Hat. Subsequent books in the series were modeled on the same requirement.