A Practice Note providing a general overview of key substantive import requirements enforced by US Customs and Border Protection (CBP). This Note discusses reasonable care under the Customs Modernization Act (Mod Act), the valuation (appraisement) of imported merchandise, tariff classification and the application of the General Rules of Interpretation (GRIs) under the Harmonized Tariff Schedule (HTS), country of origin determination and marking, partner government agencies (PGAs), recordkeeping requirements, CBP trusted trader partnership programs including the Customs Trade Partnership Against Terrorism (CTPAT), challenging CBP decisions, and CBP penalties.