Dizak , also known as Ktish after its main stronghold, was a medieval Armenian principality in the historical Artsakh and later one of the five melikdoms of Karabakh, which included the southern third of Khachen (present-day Nagorno-Karabakh) and from the 13th century also the canton of Baghk of Syunik. The founder of this principality was Esayi abu-Muse, in the 9th century. In the 16-18th centuries Dizak was ruled by the Armenian Melik-Avanian dynasty, a branch of the House of Syunik-Khachen. The seat of the princes of Dizak was the town of Togh (or Dogh) with the adjacent ancient fortress of Ktish. One of the last princes of Dizak, Esayi Melik-Avanian, was killed by Ibrahim Khalil Khan in 1781, after a long-lasting resistance in the fortress of Ktish.
Today the name "Dizak" is often used to refer to the province Hadrut of Nagorno-Karabakh Republic.