The Systems Army Epsilon was a component of the Grand Army of the Republic during the Clone Wars, one of ten such Systems Armies in total.
Comprising 294,912 clone troopers, Systems Army Epsilon was under the command of a High Jedi General, specifically a member of the Jedi High Council at this command level. This particular Systems Army was structured from two Sector Armies.
During the Clone Wars, the northern quadrant of the galaxy was the operational area for Systems Armies Delta, Epsilon, and Zeta. These three armies were further subdivided into six Sector Armies, namely: the Seventh Army, the Eighth Army, the Ninth Army, the Tenth Army, the Eleventh Army, and the Twelfth Army.