Gjerstad is a municipality located in Agder county, Norway. It is situated in the traditional region of Sørlandet in the southeastern part of the county, positioned along the border with Telemark county.
The village of Gjerstad serves as the administrative centre for the municipality. Other notable villages within its boundaries include Ausland, Eikeland, Fiane, Gryting, Østerholt, Rød, Sundebru, and Vestøl.