Secretariat of Intelligence of the State (Spanish: Secretaría de Inteligencia del Estado, mostly known by its acronym SIDE) is the premier intelligence agency of the Argentine Republic and head of its National Intelligence System.

Chaired by the Secretary of State Intelligence, a special member of the Cabinet of Ministers, the Secretariat of Intelligence was a technical and operational service charged with the collection and production of intelligence and counterintelligence in internal and foreign areas, as well as the analysis and formation of a national intelligence strategy in order to handle state affairs. The Secretariat was charged with the duty of producing a complete intelligence cycle for the government. Structurally, S.I. had the biggest intelligence-gathering capabilities in Argentina, as it has numerous delegations within Argentina as well as foreign operational bases and delegations.

Under law, the Secretariat was subordinated to the Presidency and is ruled by secret decrees and laws. Even though the official acronym was renamed to S.I. as the new intelligence system became active, during most of its history it was called Secretaría de Inteligencia de Estado (Secretariat of State Intelligence, SIDE) and it still is referred to as SIDE by the public.

On January 26, 2015, after the case of the prosecutor Alberto Nisman's death, President Cristina Fernandez de Kirchner announced she was proposing legislation that would dissolve the (SI) and opening a new intelligence agency called the Federal Intelligence Agency (AFI). President Javier Milei closed the AFI and restored the SIDE in 2024.

The Secretariat of Intelligence was created in 1946 when Juan Perón's first presidency established it by Executive Decree 337/46 under the denomination of Coordinación de Informaciones de Estado (State Intelligence Coordination, CIDE). Its mission was to act as a national intelligence agency to be run by civilian personnel and to handle foreign and domestic intelligence operations for the federal government.

Before CIDE was established, national intelligence was jointly handled by the División de Informaciones (Information Division, DI) of the Presidency, and the military intelligence services such as the Servicio de Inteligencia del Ejército (Army Intelligence Service, SIE) and the Servicio de Inteligencia Naval (Naval Intelligence Service, SIN). Even though throughout Argentina's history military intelligence organs have been involved in handling both internal and external intelligence, reforms enacted in the last few decades have legally given them a role alongside civilian managed services in the National Intelligence System.

The Secretariat (as it is commonly referred) had its first structural and functional reform in 1956, under the Pedro Aramburu government when by Executive Decree 776/56 of January 20, CIDE adopted the name Secretaría de Informaciones de Estado (Secretariat of State Information), and the subsequent famous acronym "SIDE". The newly restructured agency was closely modeled on the British intelligence system.

During Juan Carlos Onganía's government, SIDE was under the administration of General Señorans, one of the most well regarded secretaries of intelligence of all time. During those years, SIDE started to orchestrate its first complex foreign espionage missions, the staff was increased substantially to about 1,200, and the knowledge and operational capabilities were dramatically improved.