The United States has started imposing a new 10% tariff.

As of 12:01 a.m. ET on Saturday, U.S. Customs and Border Protection (CBP) began enforcing the 10% tariff imposed by President Trump on imports from numerous countries. Higher tariffs targeting 57 major trading partners are scheduled to follow next week.

This action represents a significant departure from the post-World War II framework of reciprocal tariff agreements. Kelly Ann Shaw, a trade lawyer at Hogan Lovells and former White House trade advisor, described the move as “the single biggest trade action of our lifetime.”

The announcement has already reverberated through global markets. By the close of trading on Friday, it had triggered a $5 trillion decline in the stock market valuation of 500 leading companies over two days. Oil and commodity prices also experienced sharp declines, with investors shifting capital into government bonds.

While a CBP bulletin indicated that no grace period would be granted for cargoes already en route at the time of implementation, a subsequent bulletin provides a 51-day grace period for goods loaded onto vessels or planes and in transit before 12:01 a.m. ET Saturday. The long-term economic implications of these tariffs remain to be seen.