A Civil War-era treatise addressing the power of governments in moments of emergency The last work of Abraham Lincoln’s law of war expert Francis Lieber was long considered lost—until Will Smiley and John Fabian Witt discovered it in the National Archives. Lieber’s manuscript on emergency powers and martial law addresses important contemporary debates in law and political philosophy and stands as a significant historical discovery.   As a key legal advisor to the Lincoln White House, Columbia College professor Francis Lieber was one of the architects and defenders of Lincoln’s most famous uses of emergency powers during the Civil War. Lieber’s work laid the foundation for rules now accepted worldwide. In the years after the war, Lieber and his son turned their attention to the question of emergency powers. The Liebers’ treatise addresses a vital question, as prominent since 9/11 as it was in Lieber’s lifetime: how much power should the government have in a crisis? The Liebers present a theory that aims to preserve legal restraint, while giving the executive necessary freedom of action.   Smiley and Witt have written a lucid introduction that explains how this manuscript is a key discovery in two ways: both as a historical document and as an important contribution to the current debate over emergency powers in constitutional democracies.