The Museum of Modern Art's recent redesign--the largest and most comprehensive building program in the Museum's history--embraces the changing nature of the institution and establishes it as an evolving idea, a flexible entity rather than a fixed treasure house. As the current generation of curators puts its mark on the Museum through acquisitions, exhibitions and installations, the building becomes a place where the history of art is constantly revisited, inquired into and reshaped, by its visitors as well as by its staff. <i>The Museum of Modern Art in the 21st Century</i> is an illustrated overview of an institution that is dedicated to accommodating the diversity of contemporary art and an increasingly complex and nuanced understanding of modern art. An essay by Museum director Glenn Lowry examines MoMA's current role in contemporary art as part of its long history of disrupting established paradigms, focusing on the building as a site where viewers actively experience art rather than passively receive it.