The Supreme Court Collegium is a judicial mechanism or concept for the appointment and transfer of judges in the higher judiciary, not a provision of the Constitution or an Act of Parliament. It evolved through a series of Supreme Court judgments, collectively known as the Three Judges Cases, to address the issue of executive primacy in judicial appointments.
The system's origin lies in the interpretation of the word "consultation" in Article 124 (Supreme Court appointments) and Article 217 (High Court appointments). In the First Judges Case (S. P. Gupta v. Union of India, 1981), the Court held that "consultation" did not mean "concurrence," giving the executive primacy. This was overturned in the Second Judges Case (Supreme Court Advocates-on Record Association vs Union of India, 1993), which interpreted "consultation" as "concurrence," establishing the Collegium and giving primacy to the judiciary.
The mechanism was formalized in the Third Judges Case (In re Special Reference 1 of 1998, 1998), which established the current composition for Supreme Court appointments: the Chief Justice of India (CJI) and the four senior-most Supreme Court judges. For High Court appointments, the Collegium consists of the CJI and the two senior-most Supreme Court judges. The Collegium's recommendations are sent to the President, and if the Collegium reiterates a name, the government is bound to approve the appointment.
The system faced a recent challenge when the Constitution (Ninety-Ninth Amendment) Act, 2014, and the National Judicial Appointments Commission Act, 2014, sought to replace it with the National Judicial Appointments Commission (NJAC). However, the Supreme Court struck down both in 2015 (Supreme Court Advocates-on-Record Association vs Union of India), reaffirming the Collegium system on the grounds that the NJAC violated the basic structure of the Constitution by compromising judicial independence.