From the Overview: "Japan, a U.S. treaty ally since 1951, is a significant partner of the United States in several foreign policy areas, particularly security and trade. Shared security goals range from meeting the challenge of an increasingly powerful China to countering threats from North Korea. The U.S.-Japan mutual defense treaty grants the United States the right to base U.S. troops--currently numbering around 54,000--and other military assets on Japanese territory in return for a U.S. pledge to protect Japan's security. The two countries collaborate through bilateral and multilateral institutions on issues such as science and technology, global health, energy, and agriculture. Japan is the fourth-largest overall U.S. trading partner and largest source of foreign direct investment into the United States, and its investors are the largest foreign holders of U.S. Treasury securities. The Biden Administration has emphasized the importance of restoring U.S. alliances in Asia. Former Japan Prime Minister Suga was the first in-person visitor to the White House, signaling the importance of allied cooperation. Further reinforcing Japan's central role in the U.S. approach to the Indo-Pacific, the Biden Administration has boosted the Quadrilateral Security Dialogue--or 'Quad'--convening the first-ever (virtual) leader-level meeting with Japan, Australia, and India."
CRS In Focus, IF10199
Congressional Research Service: https://crsreports.congress.gov/