Through four decades of digital initiatives and collecting programs the U.S. Library of Congress has built up a sizable digital collection. In support of long-term management of this digital content, in 2018 staff worked to review information about file extensions of content in the permanent digital collection through analysis of data in the institution’s primary digital content inventory system. This paper reports the results of this analysis and how these findings will inform the development of digital content management policy and practice at the institution.