Transaction value principle governs customs valuation, requiring invoice based price adjustments and sequential fallback valuation methods. Customs valuation uses the transaction value as the primary basis: the price actually paid or payable for goods, adjusted by specified valuation factors and subject to valuation conditions and Customs verification. When transaction value cannot be used, valuation proceeds through a prescribed hierarchy of methods. Tariff values may be fixed by the Board for certain goods. Rules specify additions and deductions to transaction value, grounds and procedures for rejecting declared values, provisional clearance against security, special procedures for related party transactions, and appeal rights with required notices and hearings.