Sarah Greenough, senior curator and head, department of photographs, National Gallery of Art. In 1990 the National Gallery of Art launched an initiative to acquire the finest examples of the art of photography and to mount photography exhibitions of the highest quality, accompanied by scholarly publications and programs. In the years since, the Gallery's collection of photographs has grown to nearly 15,000 works encompassing the history of the medium from its beginnings in 1839 to the present, featuring in-depth holdings of work by many of the masters of the art form. The Gallery's program of photography-related exhibitions and publications is now considered among the best in the world. Commemorating the 25th anniversary of this initiative, the Gallery presents three major exhibitions in 2015 exemplifying the vitality, breadth, and history of its photography holdings. Two of these exhibitions opened simultaneously on May 3, 2015: In Light of the Past: 25 Years of Photography at the National Gallery of Art and The Memory of Time: Contemporary Photographs at the National Gallery of Art, Acquired with the Alfred H. Moses and Fern M. Schad Fund. In this lecture held in honor of opening day, Sarah Greenough provides a brief history of the growth of the Gallery's photography program and an overview of both exhibitions. On view through July 26, 2015, In Light of the Past demonstrates how the Gallery's exemplary holdings reveal the evolution of the art of photography. On view through September 13, 2015, The Memory of Time explores the work of 26 contemporary artists who investigate the richness and complexity of photography's relationship to time, memory, and history.