Falk began his career as a post-doctoral researcher working first at the Stanford Linear Accelerator Center and then at the
University of California, San Diego. In 1994, he joined the physics faculty at
Johns Hopkins University, becoming a full professor in 2000. In 2006, Falk became the James B. Knapp Dean at the
Zanvyl Krieger School of Arts and Sciences at
Johns Hopkins University. From 2010 to 2017, Falk served as the 17th President of Williams College. From the beginning of 2018 until June, 2025 Falk served as President of the Alfred P. Sloan Foundation. As of July, 2025, he is the President and CEO of the Wildlife Conservation Society. ==Research==