This is the landmark judgment of Supreme Court, where in Hon’ble Justice Hans Raj Khanna has outlined the basic structure doctrine of the Constitution and that only those amendments which tend to affect the ‘basic structure of the Constitution’ are subject to judicial review.
Kesavananda Bharati Sripadagalvaru and Ors Vs State Of Kerala And Anr on 24 April, 1973Wikipedia : https://en.wikipedia.org/wiki/Kesavananda_Bharati_v._State_of_Kerala