In addition to her roles as Edward's muse and model, Jo served as the artists' record-keeper. In ledger books, now in the archives of the Whitney Museum of American Art, Jo maintained inventories of the Hoppers' works, Edward's and her own. She wrote the descriptions that accompanied Edward's pen-and-ink sketches of paintings that were turned over to the Rehn Galleries, and she recorded purchases by date, buyer, price, and commission. Jo's sketchbook—including the notes, rough drawings, and scribbled maps that she made from the passenger seat as Edward drove their Buick—documents the couple's summer driving trips in New England. Together with Jo's prolific output of diary entries and letters, these materials provide "A Window into the World of Edward and Josephine Hopper," to quote J. Anton Schiffenhaus.