Green Eggs and Ham was originally published in 1960 and according to Publishers Weekly it is the fourth-best-selling English children's book of all time. It was also voted the third out of 100 popular children's books on both the children's and teacher's list in an online survey conducted by the National Educational Association (the organization that named Dr. Seuss' birthday "Read Across America" day and March National Children's Reading Month).
The book is intentionally designed for beginning readers and in response to a bet from his publisher that he couldn't do it, Dr. Seuss wrote the entire book using only fifty different words.
The 50 are: a, am, and, anywhere, are, be, boat, box, car, could, dark, do, eat, eggs, fox, goat, good, green, ham, here, house, I, if, in, let, like, may, me, mouse, not, on, or, rain, Sam, say, see, so, thank, the, them, they, train, tree, try, will, with, would, you.
Random House, 1960, hardcover and paperback, 62 pages, ISBN: 9780394880165
Source: Wikipedia.org, "Green Eggs and Ham"