United States v. Eaton, 169 U.S. 331 (1898), was a decision of the Supreme Court of the United States involving the Appointments Clause holding that the United States Congress had the power to authorize the President of the United States to recognize a temporary diplomatic official during a period of unavailability of the congressionally approved appointee to the position.

In October 1890, Sempronius H. Boyd was commissioned as Minister Resident and Consul General of the United States to Siam.

Boyd was granted a leave of absence by the President, and before leaving Siam, Boyd asked a resident American missionary, Lewis A. Eaton, to take charge of the consulate and its archives.

The case was cited in 2017 as an argument in favor of the legitimacy of the appointment by President Donald Trump of Matthew Whitaker as Acting United States Attorney General following the resignation of Jeff Sessions from the office.

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