Customs duty levy anchored in constitutional entry and tariff schedules, with valuation governed by WTO-based rules. Entry No. 83 authorises Union legislation for customs duties; the Customs Act, 1962 levies duties with rates in the Customs Tariff Act schedules. The First Schedule uses the Harmonized System to classify imports and set rates, while the Second Schedule covers export duties. Duties are mainly ad valorem though specific and specific-cum-ad-valorem forms exist. Valuation for ad valorem duties is determined under Section 14 read with the Customs Valuation Rules, 2007, adopting the GATT/WTO valuation framework for imported and exported goods.