Registration requirement for taxable persons: PAN eligibility, voluntary registration, multiple registrations treated as distinct, and unique identity provisions. Persons liable to tax must apply for registration within the prescribed period; casual and non-resident taxable persons have an earlier application requirement. A single registration is standard, with separate registrations allowed for distinct business verticals. Voluntary registration is permitted. Eligibility requires a Permanent Account Number (or a Tax Deduction and Collection Account Number where applicable), while nonresident persons may use prescribed alternative documents. The proper officer may register defaulting persons, and certain notified international entities may receive a Unique Identity Number; registrations are granted or rejected after prescribed verification and may be deemed granted if no deficiency is communicated within the verification period.