The Act, sometimes abbreviated as ISA,[2] is introduced by the long title which states: An Act to make provision about the Secret Intelligence Service and the Government Communications Headquarters, including provision for the issue of warrants and authorisations enabling certain actions to be taken and for the issue of such warrants and authorisations to be kept under review; to make further provision about warrants issued on applications by the Security Service; to establish a procedure for the investigation of complaints about the Secret Intelligence Service and the Government Communications Headquarters; to make provision for the establishment of an Intelligence and Security Committee to scrutinise all three of those bodies; and for connected purposes.The Act placed SIS and GCHQ on a statutory footing for the first time.

[3] The Act also gives the Secretary of State for Foreign and Commonwealth Affairs the power to grant immunity from British prosecution to SIS personnel when they engage in any acts while on operations abroad that would be illegal under British law, such as murder.

[4] Section 1 of the act provides authority for the Secret Intelligence Service (MI6) to conduct intelligence activities, while Section 3 provides the similar basis for the Government Communications Headquarters (GCHQ): in the interests of national security, with particular reference to the defence and foreign policies of His Majesty's government in the United Kingdom; or in the interests of the economic wellbeing of the UK; or in the support of the prevention or detection of serious crime[5]The phrase "interests of the economic wellbeing of the UK" has been criticised by European governments as appearing to authorise industrial espionage.

[5] Disclosed by Edward Snowden in 2013: Under warrants which authorise intercepting internet traffic by tapping into fibre optic cables the Tempora program gathers all traffic flowing through the cables at the intercept point and then, using search algorithms which select material which conforms to the purposes authorised by the warrants, logs promising results for further examination.

In addition to "interests of the economic wellbeing of the UK", the purposes include "intelligence on the political intentions of foreign governments; military postures of foreign countries; terrorism, international drug trafficking and fraud.