To be effective, an army must contain the extent of desertion among its ranks. This phenomenon rose to particular prominence in Europe during the 18th and 19th centuries, with the appearance of the figure of the “citizen-soldier” on the battlefield. This paper offers the first theoretical treatment of the issue of desertion from an economic perspective. Building on the work of Yoram Barzel on the “economic analysis of property rights,” we develop a “desertion as theft” framework. We then test the empirical implications of the framework against qualitative and quantitative evidence from Napoleonic France.