Todd's writing concerns literature and culture of the Restoration and eighteenth and early nineteenth centuries. Over a long career she has published more than 35 critical and biographical books and collections of essays, mainly on women authors, women's writing, cultural history and the development of fiction. She has edited full-scale editions of Mary Wollstonecraft (with Marilyn Butler) and Aphra Behn, as well as individual works of women such as Charlotte Smith, Helen Maria Williams, Mary Shelley, Mary Carleton and Eliza Fenwick.