The collegium system is one where the Chief Justice of India and a forum of four senior-most judges of the Supreme Court recommend appointments and transfers of judges. However, it has no place in the Constitution.
The system was evolved through Supreme Court judgments in the Three Judges Cases: S.P. Gupta case (December 30, 1981) or the First Judges Case: It declared that the “primacy” of the CJI’s recommendation on judicial appointments and transfers can be refused for “cogent reasons.” The ruling gave the Executive primacy over the Judiciary in judicial appointments for the next 12 years.
Supreme Court Advocates on Record Association versus Union of India or the Second Judges Case(October 6, 1993): The majority verdict gave back CJI’s power over judicial appointments and transfers. It says the CJI only need to consult two senior-most judges. “The role of the CJI is primal in nature because this being a topic within the judicial family, the Executive cannot have an equal say in the matter,” the verdict reasoned. However, confusion prevails as the CJIs start taking unilateral decisions without consulting two colleagues. The President is reduced to only an approver.
In Special Reference case of 1998 or the Three Judges Case (October 28, 1998): On a reference from former President K.R. Narayanan, the Supreme Court lays down that the CJIs should consult with a plurality of four senior-most Supreme Court judges to form his opinion on judicial appointments and transfers.