The story of dealers of Old Masters, champions of modern art, and victims of Nazi plunder. In Belonging and Betrayal, distinguished historian Charles Dellheim tells the story of the rise and fall of a small number of Jews, individuals, and families, who were merchants and connoisseurs as well as dealers and collectors of fine art. They competed and cooperated at various times and operated more often than not on both sides of the Atlantic. The protagonists of this story took a leading part in the critical transformations that shook the art world in the late nineteenth and early twentieth centuries: the great migration of Old Master paintings from Europe to the United States; and the eventual triumph of modern art as Jewish dealers became the modernists' champions. The story begins with the entry of Jewish dealers into the art world in the late nineteenth century and ends with the Nazi plunder of their collections. Along the way, the narrative takes us into a variety of European capitals--Paris, London, Berlin, and Vienna--as well as American cities, notably Boston and New York. It sets the protagonists' stories against the backdrop of the broader changes that affected their fortunes and transformed art and society: The gradual opening of high culture, the dynamics of assimilation, acculturation, and antisemitism, the decline of the landed classes, the ascent of a new capitalist elite, the cultural impact of the "Great War," and the Nazi war against the Jews.