The Intelligence Bureau (IB) is India's internal security and counterintelligence agency under the Ministry of Home Affairs. It was founded in 1887 as the Central Special Branch. The IB is often regarded as the oldest extant intelligence organisation in the world.

Until 1968, it handled both domestic and foreign intelligence after which the Research and Analysis Wing was formed specifically for foreign intelligence; following that, the IB was primarily assigned the role of domestic intelligence and internal security. Tapan Deka is the current director of the IB, since June 2022.

The Intelligence Bureau traces its origin to the Central Special Branch, established on 23 December 1887 by the British government in India to gather intelligence on political unrest, particularly after the formation of the Indian National Congress in 1885. Its creation followed Secret Dispatch No. 11, dated 25 March 1887, in which R. A. Cross, the Secretary of State for India, sanctioned the proposal by Marquess of Dufferin, the Viceroy of India, to create a system for the "collection of secret and political intelligence in India".

Dufferin proposed utilizing the police forces in British India and political officers in princely states for the "collection of intelligence on political, social and religious movements". He recommended the establishment of "special agencies" at both central and provincial headquarters, assigning local governments the responsibility of intelligence collection and obliging them to report relevant findings to the central government. The Provincial Special Branches, under local government control, were tasked with sharing intelligence with the Central Special Branch.

Dufferin modelled the agency after the Third Section of Imperial Russia. To reduce expenses, the agency shared the manpower and facilities of the existing Thuggee and Dacoity Department, headquartered at Shimla. The General Superintendent of the Department was entrusted with the supervision of the Central Special Branch. His proposed annual budget was ₹46,800. Donald McCracken, a police officer from the Punjab cadre, was appointed as its first head. McCracken was the assistant to the General Superintendent, Colonel P. D. Henderson. The Provincial Special Branches were attached to the offices of either the Inspector General of Police or the chief secretary of the respective provinces.

In 1904, based on the recommendations of the Indian Police Commission (1902 – 1903) chaired by Andrew Fraser, the Central Criminal Intelligence Department—also known as the Department of Criminal Intelligence (DCI)—was established. This reorganization led to the abolition of the Thuggee and Dacoity Department and the merger of the Central Special Branch into the DCI. Additionally, Criminal Investigation Departments (CID) were created in the provinces. Initially, Provincial Special Branches were incorporated into the CIDs, headed by a Deputy Inspector General (DIG), but they were later separated as their functions evolved.

Section 40(2) of the Government of India Act 1919 stated that "the Intelligence Bureau should keep the Government posted with matters relating to the security of the Indian Empire." Reflecting this directive, the DCI was renamed the Intelligence Bureau in 1920, a year before the Act formally came into force in 1921. In the 1920s, the IB's role was reduced to primarily relaying intelligence to the Indian Political Intelligence (IPI) office in London, which was responsible for analyzing intelligence, and acted as a liaison between the IPI and the Government of India. Following the implementation of provincial autonomy under the Government of India Act 1935, the IB began assigning officers designated as Central Intelligence Officers to the provinces starting in 1937.

The IB, initially also referred to as the Delhi Intelligence Bureau (DIB), was placed under the Home Department and reported directly to the Governor-General of India. After India gained independence in 1947, the IB came under the Ministry of Home Affairs, with T. G. Sanjeevi Pillai becoming its first Indian director. Until 1968, the IB was responsible for both internal and external intelligence. However, shortcomings in its external intelligence, particularly in foreseeing Chinese movements before the Indo-China War of 1962 led to the creation of the Research and Analysis Wing (R&AW) in 1968, dedicated to external intelligence.