(written from a Production point of view)
Grosset & Dunlap is a publishing company founded in 1898. In 1972, the company acquired Ace Books, and in 1982, the two divisions became subsidiaries of G.P. Putnam's Sons, and eventually fell under the Penguin umbrella.
The imprint is now used for young adult novels and series including The Hardy Boys, Nancy Drew, Tom Swift, The Bobbsey Twins, Dragon Slayers' Academy, and Hank Zipzer.