Desertion was significant drain on the British Army’s slender manpower resources during the Napoleonic Wars, despite severe military justice that could inflict capital punishment for this military crime. This article explores the reasons why soldiers left the Army, and it argues that there were three main wellsprings of desertion: adjustment to life as a soldier; discontent with the service; and opportunities beyond the service. These factors underlay soldiers’ decisions to leave the Army, but location also played a crucial aspect, either facilitating or suppressing desertion. These causes and influences explain the incidence of desertion at a macro level and also the wide variations in absence rates between individual units. Moreover, desertion demonstrates that soldiers had both a strong sense of their rights—attitudes that were transferred from their civilian lives—and continued connections with civilian society.