The stated mission is to confront and address securitythreats, including international terrorism, foreign subversion and espionage. The ISD also monitors and addresses potential threats from communism, prevention of racial tension which might affect the public peace, domestic counterterrorism, international counterterrorism, fraud against the state, surveillance, apprehension of suspected militants or terrorists and protection of Singapore's national borders.
ISD was first established as part of the Special Branch in 1948 by the British colonial government. In 1963, it became part of the Malaysian Special Branch when Singapore joined Malaysia. After Singapore gained independence, Internal Security Department was formally established on 17 February 1966. It was formerly part of the Ministry of Interior and Defence until it was split on 11 August 1970.
1997, 1998, six arrested for involvement in espionage and foreign subversive activities.
2001, 9 December, members of Jemaah Islamiyah (JI) arrested for bomb plots on the American, Australian, British and Israeli embassies.
2008, 27 February, Mas Selamat bin Kastari, alleged leader of JI's Singapore branch, escaped while under the ISD's custody.
2009, 1 April, the Malaysian authorities captured Mas Selamat in Skudai, Johor.
2010, 8 February, the ISD summoned Pastor Rony Tan of Lighthouse Evangelism over video clips posted on the church website that were deemed 'highly inappropriate and unacceptable' as they "trivialised and insulted the beliefs of Buddhists and Taoists".
2021, 27 January, the ISD reported it had arrested a 16-year old Protestant youth under the Internal Security Act in November 2020 for plotting to attack two Singaporean mosques on the anniversary of the 2019 Christchurch mosque shootings. The youth had written a manifesto praising the perpetrator Brenton Tarrant as a "saint" and describing the Christchurch mosque shootings as the "justifiable killing of Muslims." The teenage is the youngest person and the first far right extremist to be detained under the ISA.
2021, 29 January, Yeo Jun Wei, was detained by the ISD for investigations into engaging in "activities prejudicial to Singapore’s security".
Mathew Jones, "Creating Malaysia: Singapore Security, the Borneo Territories and the Contours of British Policy, 1961–1963" in Journal of Imperial and Commonwealth History, Vol. 28, No. 2, May 2000. pp. 85–109