GST registration liability applies where suppliers' aggregate turnover crosses the applicable threshold, with special state concessions. Suppliers must register under the Act when their aggregate turnover in a financial year exceeds the statutory threshold, with a lower threshold for supplies from special category States. Persons registered or licensed under prior law immediately before the appointed day must register from that day. Transfer of a registered business as a going concern makes the transferee or successor liable to register from the date of transfer; transfers consequent on sanctioned amalgamation or demerger require registration from the date the Registrar of Companies issues the incorporation certificate. Aggregate turnover includes supplies on own account or on behalf of principals; job worker supplies after job work are treated as supplies by the principal.