The Onderon Resistance, or Onderon underground, referred to the local resistance movement on the planet of Onderon during the Galactic Civil War.
In 2 ABY, they assisted the Alliance to Restore the Republic in the attack of an Imperial military ordnance center on Onderon. They made heroic efforts to destroy the sensor nets and planetary shields before the Rebel attack, allowing the Rebels ships to destroy the base with minimal loses.