Entry into force of tax treaty requires mutual notification; treaty applies to tax years commencing after that notification. Entry into force is effected when the Contracting States notify each other that constitutional requirements are met; the Convention applies from that notification date and, for New Zealand, to income years beginning on or after the first 1 April in the calendar year following entry into force, and for India, to previous years for income-tax purposes beginning on or after the first 1 April in the calendar year following entry into force.