Registration requirement under GST mandates timely application, PAN/TAN eligibility and single or vertical-specific registrations with verification. Persons liable to GST must apply for registration within prescribed timelines, with casual and non-resident taxable persons required to apply before commencing business; supplies from territorial waters are registered at the State of the nearest baseline. Registration is generally single but separate registrations may be allowed for distinct business verticals; voluntary registration subjects persons to all registered-person obligations. Eligibility requires a Permanent Account Number (or TAN where applicable), while non-resident persons may use other prescribed documents. Officers may register defaulters; notified international and diplomatic entities may receive a Unique Identity Number; registrations are verified, certified, and deemed granted after prescribed periods.