Horton Hatches the Egg is a children's book written and illustrated by Theodor Geisel under the pen name Dr. Seuss and published in 1940 by Random House.

The book tells the story of Horton the Elephant, who is tricked into sitting on a bird's egg while its mother, Mayzie, takes a permanent vacation to Palm Beach.

He found elements of Horton in earlier Dr. Seuss works, most notably the 1938 short story "Matilda, the Elephant with a Mother Complex".

The book centers on a genial elephant named Horton, who is convinced by Mayzie, an irresponsible and lazy bird, to sit on her egg while she takes a short "break", which turns into her permanent relocation to Palm Beach.

As Horton sits in the nest on top of a tree, he is exposed to the elements, laughed at by his jungle friends, captured by hunters, forced to endure a terrible sea voyage, and finally placed in a traveling circus.

She visits the circus just as the egg is due to hatch (after 51 weeks in Palm Beach) and demands that Horton should return it, without offering him a reward.

According to Geisel's biographers Judith and Neil Morgan, Horton Hatches the Egg was born in 1940, the day after New Year's, when he took a break from drawing in his Park Avenue apartment and went for a walk.

When he returned, he noticed that he had left a window open in his studio and that the wind had blown one sketch on transparent paper on top of another, making it look like an elephant was sitting in a tree.

In an early installment of Geisel's cartoon feature "Boids and the Beasties", which began in Judge magazine in 1927, he juxtaposed a bird and an elephant.

[7] Frances Chrystie, the juvenile buyer for FAO Schwarz, wrote to Bennett Cerf, Geisel's publisher, "I've been sitting alone in my apartment reading Horton aloud to myself over and over again...

[13] Geisel responded to Lurie's criticism, by way of his biographers near the end of his life, by remarking that most of his characters are animals, noting, "if she can identify their sex, I'll remember her in my will.

Deans draws a connection between the elephant-bird in Horton and the Infantograph, a failed invention Geisel created that combined two photos and was meant to give couples an idea of what their children would look like.

[15] Richard B. Freeman, writing in 2011 about the contemporaneous economic situation in the United States, called Horton Hatches the Egg a tale of investment.

"[16] The book was adapted into a ten-minute animated short film by Leon Schlesinger Productions and released in 1942 as part of Warner Bros.' Merrie Melodies series.

[18] In 1992, Random House released "Horton Hatches the Egg" in its series of Dr. Seuss videos, narrated by Billy Crystal and directed by Mark Reeder.