Transaction value determination governs customs pricing, with specified additions and rule-based alternatives when transaction value is inapplicable. Customs valuation is based on the transaction value-the price actually paid or payable where buyer and seller are unrelated and price is the sole consideration-with specified additions for costs and services for imports. Rules set related-party criteria, alternative valuation methods when transaction value is inapplicable, procedures for challenging declared values, and require use of the exchange rate prevailing on the declaration date. Importers must declare value, produce invoices, and file valuation declarations to permit assessment.