The Collegium System is a judicially-evolved concept for the appointment and transfer of judges to the higher judiciary in India, which is not explicitly mentioned in the Constitution. Its origin lies in a series of three Supreme Court judgments, collectively known as the Three Judges Cases, which sought to address the executive's dominance in judicial appointments.
The system was created to solve the problem arising from the First Judges Case (S. P. Gupta v. Union of India, 1981), which had ruled that the word "consultation" in Article 124(2) and Article 217(1) did not mean "concurrence," giving the executive primacy. The Collegium System was established by the Second Judges Case (Supreme Court Advocates-on Record Association v. Union of India, 1993), which overruled the 1981 decision and held that "consultation" must mean "concurrence," transferring primacy to the judiciary.
The mechanism for the Supreme Court Collegium, which handles appointments and transfers for the Supreme Court and High Courts, consists of the Chief Justice of India (CJI) and the four senior-most judges of the Supreme Court. This composition was clarified in the Third Judges Case (In re Special Reference 1 of 1998), which mandated that the CJI must consult a plurality of four senior-most judges. The President of India formally makes the appointment, but is bound to approve the recommendation if the Collegium reiterates it after reconsideration.
The system connects directly to the constitutional provisions for judicial appointments in Article 124 and Article 217. The most significant recent challenge was the attempt to replace it with the National Judicial Appointments Commission (NJAC), established by the 99th Constitutional Amendment Act, 2014, which introduced Article 124A. However, the Supreme Court struck down the NJAC Act in October 2015, ruling that it violated the basic structure of the Constitution by compromising judicial independence, thus ensuring the Collegium System remains the current mechanism.