A Practice Note discussing the investigations under Section 232 of the Trade Expansion Act of 1962 regarding the impact of imports of steel and aluminum on US national security, which were conducted by the US Department of Commerce's Bureau of Industry and Security (BIS) during the Trump administration. This Note discusses the tariffs imposed by the Trump administration on steel and aluminum imports under Section 232, country exemptions, the Biden administration's replacement of tariffs on certain countries' exports with tariff-rate quotas (TRQs), the process for US companies to request the exclusion of particular products from the tariffs, and the responses of other countries to these tariffs, including retaliatory duties and challenges at the World Trade Organization (WTO).