Registration requirement: suppliers making taxable supplies must obtain GST registration when aggregate turnover exceeds the statutory threshold. Suppliers making taxable supplies in the State must obtain registration when their aggregate turnover in a financial year exceeds the prescribed threshold, subject to the Bengal Eastern Frontier Regulation, 1873 and relevant governmental orders. Persons registered under existing law on the day before the appointed day must be registered from the appointed day. Transfers of a registered business as a going concern require the transferee or successor to register from the date of transfer, and transferees under court-sanctioned amalgamation or de-merger must register from the Registrar of Companies' certificate date. The section clarifies inclusion of supplies on behalf of principals, treatment of job worker supplies, and the meaning of special category States.