The Council for National Security (Thai: คณะมนตรีความมั่นคงแห่งชาติ; RTGS: Khana Montri Khwam Man Khong Haeng Chat; abbreviated CNS (Thai: คมช.), was the military junta that ruled Thailand between its coup d'état against Prime Minister Thaksin Shinawatra on 19 September 2006 until the later coup d'état on 22 May 2014. Thaksin was deposed while overseas in New York City in a nonviolent coup led by Royal Thai Army (RTA) Commander General Sonthi Boonyaratglin, one of Thailand's top military commanders. Martial law was declared on 19 September by General Sonthi, who stated that the action was taken in an effort to "bring back normality and harmony" and with the intent to "return power to the Thai people as soon as possible." This sentiment was echoed by King Bhumibol Adulyadej, who subsequently appointed General Sonthi to lead the governing council.

General Sonthi led the Council, acting as both the prime minister and the cabinet, until the appointment of General Surayud Chulanont as the new prime minister. However, the Council retained considerable political power under the Council-drafted 2006 Interim Constitution, especially concerning the drafting of a permanent constitution.

The Council was dissolved on 22 May 2014 upon the partial repeal of the 2007 Constitution of Thailand, when Army Commander General Prayut Chan-o-cha launched a coup d'état in response to six months of political crisis. It was succeeded in its capacity as military junta by the National Council for Peace and Order.

The Council was originally formed as the Council for Democratic Reform (Thai: คณะปฏิรูปการปกครองในระบอบประชาธิปไตยอันมีพระมหากษัตริย์ทรงเป็นประมุข; RTGS: Khana Patirup Kanpokhrong Nai Rabop Prachathippatai An Mi Phramahakasat Songpenpramuk), abbreviated to CDR (Thai: คปค.). The Council's original Thai name translates literally to "Council for Reforming the Democratic Regime of Government with the King as Head". On 21 September 2006, a spokesperson requested the local media to report the Council's English name in full, rather than shortening it, along with the addendum "under the Constitutional Monarchy" after news reports had been shortening the name in their coverage. This was because the Council felt that its full name was significant to relaying its intended message, and that the shortened version may be "misleading".

However, on September 27, the Council announced that they would be dropping the English reference to the monarchy due to misunderstandings arising by foreign media concerning the role the monarchy played in the Council, and declared that it would officially be known as the Council for Democratic Reform in English. When the 2006 interim constitution was released that same day, ahead of its promulgation on October 1, it included articles creating a Council for National Security with an identical leadership to that of the CDR, effectively re-naming the CDR to the Council for National Security once the interim constitution came into effect.

Sonthi received the appointment and blessing of king Bhumibol Adulyadej, who is quoted as saying, "So as to maintain peace and order in the nation, His Majesty the King has graciously granted a Royal Command appointing General Sonthi Boonyaratglin as Leader of the Council for Democratic Reform. The people is requested to remain calm while all public servants are to follow Orders issued by General Sonthi Boonyaratglin, henceforth onwards." The junta consists of the leaders of all branches of the Thai military and police:

A week after the coup, Sonthi's former classmate Gen Boonsrang Naimpradit was promoted from Deputy Supreme Commander to the post of Supreme Commander, replacing Ruangroj Mahasaranon. Junta Secretary General, Winai Phattiyakul, was promoted to the post of Permanent Secretary for Defence.

Gen Sonthi also promoted his classmates and lieutenants in the coup, 1st Army Region Commander Lt-Gen Anupong Paochinda and 3rd Army Region Commander Lt-Gen Saprang Kalayanamitr, to the post of Assistant Army Commander.