Philip Dey "Phil" Eastman was an American screenwriter, children's author, and illustrator. As an author, he is known primarily as P. D. Eastman. A protégé of Theodor Geisel (Dr. Seuss), Eastman wrote many books for children, in his own distinct style under the Dr. Seuss brand of Random House, many of which were in the Beginner Books series.

From 1936 to 1941, Eastman worked at the story department of Walt Disney Productions. From 1941 to 1943 he worked at the story department of Warner Bros. Cartoons. From 1945 to 1952 he worked in the story department of United Productions of America. He contributed to the "Private Snafu" World War II training films, wrote for the animation Mr. Magoo, and the Gerald McBoing-Boing series for UPA.