Inter-Services Intelligence (ISI) is the largest intelligence agency in Pakistan. The headquarters of ISI is situated in Islamabad. It was founded in 1948. It is estimated that the ISI has over 25,000 employees with another 30,000 working as informants and other roles. The current director of the ISI is Faiz Hameed. 
The Inter-Services Intelligence was founded in 1948 by Robert Cawthorne who was a British Army officer.  It was later expanded by Pakistani Military dictator Ayub Khan in the 1950's.
- Joint Intelligence X -serves as a secretariat which coordinates and provides administrative support to the other branches of the ISI. It prepares intelligence estimates and threat assessments.
- Joint Intelligence Bureau -is responsible for political intelligence. It consists of 3 subsections, one of which is dedicated to operations against India.
- Joint Counter-Intelligence Bureau - is responsible for surveillance of Pakistani diplomats working abroad. It also conducts operations in the Middle East, South Asia, China, Afghanistan and the Central Asian republics.
- Joint Intelligence/North -responsible for conducting infiltration, exfiltration, propaganda and other clandestine operations inside the Indian state of Jammu and Kashmir.
- Joint Intelligence Miscellaneous -conducts espionage in foreign countries, which includes offensive intelligence operations.
- Joint Signal Intelligence Bureau -operates a chain of signals intelligence collection stations along the border with India. Additionally, it provides communication support to Islamic terrorists operating in India.
The ISI also has separate explosives and chemical warfare sections. 
- The ISI is given the task of collecting foreign and domestic intelligence; co-ordination of intelligence functions of the 3 military services; surveillance over its cadre, foreigners, the media, politically active segments of Pakistani society, diplomats of other countries accredited to Pakistan and Pakistani diplomats serving outside the country;the interception and monitoring of communications; and the conduct of covert offensive operations.
- Diplomatic Missions- Provides an ideal cover and ISI operation centers are generally located on the embassy or consulate premises.
- Multinationals- ISI operatives find good cover in multinational organizations. NGO's and cultural programs also function as popular covers to shield ISI activites.
Involvement in the 9/11 Attacks
- On July 14, 1999, a U.S government informant by the name of Randy Glass, recorded a conversation at a dinner attended by himself, illegal arms dealers Diaa Mohsen and Mohammed Malik, a former Egyptian judge by the name of Shireen Shawky and Pakistani ISI agent Rajaa Gulum Abbas. The dinner was held at a restaurant within view of the World Trade Center. FBI agents, pretending to be customers, were seated at nearby tables. Abbas, stated that he wanted to buy a whole shipload of weapons, stolen from the U.S military to give to Osama Bin Laden. Abbas then pointed to the World Trade Center, saying, "Those towers are coming down." Later on, Abbas makes 2 other references to an attack on the World Trade Center, saying, "Americans [are] the enemy," and "We would have no problem blowing up this restaurant because it is full of Americans."
- On August 17, 1999, the same group that met in a New York restaurant this time meets at a warehouse in West Palm Beach, Florida. The group is shown Stinger missiles as part of a sting operation. U.S intelligence soon discovers connections between two individuals in the group, Rajaa Gulum Abbas and Mohammed Malik, Islamic terrorist groups in Kashmir(backed by the ISI against India), and the Taliban. Mohammed Malik suggests during the meeting that the Stingers will be used in Kashmir or Afghanistan. Diaa Mohsen, the colleagues of Malik, says that Abbas has direct connections to "dignitaries" and Osama Bin laden. Abbas wanted heavy water for a "dirty bomb" or other material to build a nuclear weapon. Abbas said that he will bring a Pakistani nuclear scientist to inspect the material. According to Dick Stoltz, a government undercover agent who posed as an illegal arms dealer, one of the Pakistanis working at the warehouse claimed he was working for Abdul Qadeer Khan. Khan is considered to be the father of Pakistan's nuclear weapons program and is also the head of an illegal network which sells nuclear technology technology to rogue states. U.S government informant Randy Glass tried to pass these warnings on to higher levels of the government, but he claimed that, "The complaints were ordered sanitized by the highest levels of government."
- Profile: Pakistan's military intelligence agency BBC