Mary Pope Osborne wrote her first book in 1982, entitled "Run, Run, as Fast as You Can". She wrote the first Magic Tree House book in 1992, entitled Dinosaurs Before Dark. During those ten years, she wrote many other books, and aimed toward younger audiences.
From 1993 to 1997, she served as the 27th President of the Author's Guild. She has been writing a full series of Magic Tree House books since 1992, and book #40, Eve of the Emperor Penguin was released just in September. That will follow book #41 Moonlight on the Magic Flute, released in Spring 2009.
Mary Pope Osborne is also organizing a musical, called Magic Tree House: The Musical.