In the series, the title character is a talking mouse who lives in New Mouse City on Mouse Island. A best-selling author, Geronimo Stilton works as a journalist and editor for the fictional newspaper The Rodent's Gazette.
He has a younger sister named Thea Stilton, a cousin named Trap Stilton, and a favorite little nephew, nine-year-old Benjamin Stilton. Geronimo is a nervous, mild-mannered mouse who would like nothing better than to live a quiet life, but he keeps getting involved in far-away adventures with Thea, Trap, and Benjamin, and sometimes Aunt Sweetfur. The books are written as though they are autobiographical adventure stories.
The series originated in Italy and has become the most popular children's book series in that country. The books have been translated into 35 languages.
Papercutz obtained the rights to publish English translations of the graphic novels of Geronimo Stilton. These retain some of the original names of the characters that were changed in the storybooks translated by Scholastic. For example, the English translations of the graphic novels by Papercutz continue to use the names "Patty Spring" and "Pandora", while the storybooks by Scholastic changed these names to Petunia Pretty Paws and Bugsy Wugsy, respectively.