To "honor significant and enduring contributions to American society, history, culture or environment" on stamps, the United States Postal Service has featured American art in various contexts. In 1940, five 19th-century artists were included in the Great Americans series, while the 1998 panel, Four Centuries of American Art, highlighted twenty paintings.  In between, statehood commemoratives featured artists such as Grant Wood and Edward Hopper.  More recently, the USPS has issued panels celebrating Mary Cassatt, Andrew Wyeth, Isamu Noguchi, and Romare Bearden to reflect our national identity.