Desertion (military), offense of abandoning military service by one in such service. The term is also used to describe the actions of those who leave a post to avoid hazardous duty or to shirk important assignments. In time of peace, desertion is punishable by imprisonment or other penalties except death. In time of war, punishment for desertion in almost all countries may be death. Courts-martial of the U.S. Army during World War II often punished offenders instead for absence without official leave (AWOL), even after an absence of as long as eight months.

In the merchant marine service, absence without leave for 48 hours is regarded as conclusive evidence of desertion and is punishable by discharge. When desertion occurs on government-owned merchant ships in time of war, the offenders are liable to fine or imprisonment.