Three rules, not one
People tend to lump these together because they all touch sourcing, but they come from different laws, apply in different situations, and get checked in different ways. Knowing which one governs a given contract matters more than knowing the general idea of buying American.
Buy American: a domestic-content preference
The Buy American Act creates a preference for domestic end products and construction materials on U.S. government purchases, generally requiring a product to be manufactured in the United States and to meet a domestic-content threshold for its components. The exact percentage thresholds have shifted in recent years and continue to be adjusted, so check the specific clause in your solicitation rather than relying on a remembered number. It is a preference with exceptions, not an absolute bar on foreign content, and agencies can waive it in specific circumstances.
The Trade Agreements Act: a different test on larger buys
The Trade Agreements Act, TAA, applies above certain dollar thresholds and works differently: instead of a domestic-content percentage, it requires the end product to be substantially transformed in the United States or in a country that has a qualifying trade agreement with the U.S. A product can fail Buy American's content math and still pass TAA, or the reverse, because the two are not testing the same thing. When a solicitation cites TAA, ask your supplier where final substantial transformation happens, not just where parts are sourced.
Section 889: about your own operations, not just what you sell
Section 889 is different in kind from the other two. It restricts the government from contracting with companies that use certain specifically named Chinese telecommunications and video surveillance equipment, and equipment from their affiliates, in their own internal systems, not just in what they deliver. Representing compliance means checking your own network equipment, cameras, and related infrastructure, including at your subcontractors, not only auditing your product's bill of materials.
What you are actually certifying
Solicitations typically require you to represent your compliance with these rules directly in your offer, often through standard representations and certifications language. Signing that representation without having actually checked your supply chain and your own equipment is the real risk, not the rule itself. Ask suppliers directly where components are made and substantially transformed, keep their answers on file, and walk your own IT and facilities equipment against the Section 889 restrictions before you certify anything.
When you are not sure
These rules carry enough edge cases, waivers, and exceptions that a specific answer for a specific contract is worth getting from the contracting officer or a qualified advisor rather than guessing. General guidance and current rules are maintained at acquisition.gov.