The Central Bureau of Investigation (CBI) is India's premier investigating agency, responsible for a wide range of criminal and national security-related cases. It operates under the jurisdiction of the Ministry of Personnel, Public Grievances and Pensions, Government of India, and derives its powers from the Delhi Special Police Establishment Act, 1946.

Composition: The CBI is headed by a Director, who is an IPS officer of the rank of Director General of Police (DGP). The Director is appointed by a high-powered committee comprising the Prime Minister (as Chairperson), the Leader of Opposition in the Lok Sabha (or the leader of the single largest opposition party), and the Chief Justice of India (or a Supreme Court Judge nominated by the CJI). This selection process aims to ensure the independence of the agency's head.

The CBI comprises several specialized divisions, each with distinct functions:

1. Anti-Corruption Division: Investigates cases of corruption and fraud against public servants of the Central Government, Public Sector Undertakings, and financial institutions.
2. Economic Offences Division: Deals with major financial scams, bank frauds, cybercrime, import-export and foreign exchange violations, and other sophisticated economic crimes.
3. Special Crimes Division: Investigates serious and sensational crimes like murder, kidnapping, terrorism, and organized crime, when referred by the Central Government, State Governments, or ordered by the Supreme Court or High Courts.
4. Policy & International Police Cooperation Division: Handles policy matters, coordinates with Interpol, and facilitates international investigations.
5. Administration Division: Manages the internal administration, logistics, and personnel of the CBI.
6. Directorate of Prosecution: Provides legal advice and handles the prosecution of cases investigated by the CBI.
7. Central Forensic Science Laboratory (CFSL): Provides scientific and forensic support to investigations.

The agency is staffed by officers drawn from various central police organizations, state police forces, and other government departments on deputation, as well as its own cadre.

Functions: The primary functions of the CBI include:

• Investigating Anti-Corruption Cases: Probing cases of bribery, corruption, and misconduct by Central Government employees and those in public sector undertakings.
• Investigating Economic Crimes: Tackling large-scale financial frauds, cheating, counterfeiting, drug trafficking, and other economic offenses.
• Investigating Special Crimes: Handling serious and sensational crimes of national or international ramifications, often referred by courts or governments.
• Coordinating with State Police: Assisting state police forces in complex cases and coordinating inter-state and international investigations.
• Maintaining Crime Statistics: Collecting and disseminating criminal intelligence and maintaining records of crime.
• Research and Training: Conducting research on crime patterns and providing training to its officers and other law enforcement agencies.
• Acting as the National Central Bureau for Interpol: Serving as the nodal agency for all Interpol matters in India.

While the CBI plays a crucial role in maintaining law and order and combating serious crime, it often faces challenges related to political interference, resource constraints, and the need for state government consent for investigations within their jurisdiction, which can sometimes impede its effectiveness.