An army of observation is a military body whose purpose is to monitor a given area^[1] or enemy body in preparation for possible hostilities.

Some of the more notable armies of observation include:

• Third Reserve Army of Observation, a Russian army tasked to monitor the Austrian border in 1811 prior to the French invasion of Russia
• The army of observation at Fort Jesup, Louisiana, United States, which monitored Texas' transition from Spanish to Mexican control, and to eventual independence
• The Hanoverian Army of Observation which monitored the border prior to the French Invasion of Hanover in 1757