Museums work constantly to improve their collections and ways of displaying them. All museums share a common aim -to attract visitors and help them to understand and enjoy the collections. Museums are always on the watch for new additions to their collections. Works of art are bought from art dealers and private collectors or at auction sales. Museums also accept gifts and bequests, but the large museums no longer accept everything that is offered to them. They accept only objects or collections that meet their high standards. Museums often arrange loan exhibitions of important works from private owners, art dealers, and other museums. In this way a famous masterpiece may be viewed by people who otherwise might never have the chance to see it. For example, in 1963 the Metropolitan Museum of Art in New York City exhibited one of the world's most famous ladies -Mona Lisa, painted by Leonardo da Vinci. The government of France had lent the painting to the United States.