The Iga ikki, full name Iga Sokoku Ikki, also known as the Iga Republic, Iga Confederacy, or Iga Commune, was a republic-style military confederation of ninjas based in Iga Province during the Sengoku period of Japan. One of the two major schools of ninjutsu, Iga-ryū, is attributed to, and takes its name, from this confederation. During the second half of the 15th century, the ninja families in Iga formed a military confederacy dedicated to the defense of the province. After centuries of rivalry with its northern neighbor, Kōka District in Ōmi Province, eventually Iga worked closely with in alliance with Kōka. In the 16th century, a constitution was drafted based on principles of mutual defense and voluntary association. The confederacy produced legendary figures such as Momochi Sandayu, Fujibayashi Nagato, Hattori Hanzō, Tateoka Doshun, and Shimotsuge no Kizaru. The activities of Iga eventually drew the ire of the Oda clan, who launched invasions in 1579 and 1581. The first invasion was decisively repelled by Iga, but the second overwhelmed the Iga forces and Oda Nobunaga viciously destroyed the confederation. Some ninja were spared and their activities allowed to continue. After Nobunaga's assassination in 1582, Iga and Kōka ninja, under the leadership of Hanzō, provided services to Nobunaga's ally Tokugawa Ieyasu and his descendants into the Tokugawa shogunate.

A ninja or shinobi was a covert agent, mercenary, or guerrilla warfare expert in feudal Japan. The functions of a ninja included siege and infiltration, ambush, reconnaissance, espionage, deception, and later bodyguarding and their fighting skills in martial arts, including ninjutsu. Their covert methods of waging irregular warfare were deemed dishonorable and beneath the honor of the samurai. Though shinobi proper, as specially trained warriors, spies, and mercenaries, appeared in the 15th century during the Sengoku period, antecedents may have existed as early as the 12th century.