GST registration obligation establishes legal supplier status and input tax credit entitlement, with distinct rules for special taxable persons. Registration under GST confers legal recognition, enables collection of tax and claiming of input tax credit, and is mandated based on a supplier's aggregate turnover and specified categories; casual and non resident taxable persons, ISDs, and inter state suppliers face distinct registration rules, validity periods, advance deposit and return obligations. Administrative procedures cover application, amendment, rejection, cancellation and revocation, with PAN requirements, e signature options, prescribed timelines for authority action, and consequences on cancellation including reversal of input tax credits.