The Formosa Resolution was a bill enacted by the U.S. Congress on January 29, 1955 that established an American commitment to defend Formosa (now called Taiwan). As a matter of American foreign policy, President Dwight D. Eisenhower promised to protect "territories in the West Pacific under the jurisdiction of the Republic of China" (i.e. Taiwan and Penghu) against invasion by the People's Republic of China (PRC). The legislation provided the President with the power to intervene if the island was attacked.
The legislation was prompted, in part, by attacks on the islands of Kinmen and Matsu in the Taiwan Strait by the Chinese People's Liberation Army in 1954. Both islands had been held by the Kuomintang government of Republican China under Chiang Kai-shek, which had been handed the island of Taiwan in 1945.
Following the enactment of the Formosa Resolution, the PRC and the US successfully negotiated an agreement to stop the bombing of the islands in the Taiwan Strait. This peaceful result ended the First Taiwan Strait Crisis.
Both the House and Senate approved this resolution: 85 to 3 in the Senate and 409 to 3 in the House.
This resolution expires "when the President shall determine that the peace and security of the area is reasonably assured by international conditions created by action of the United Nations or otherwise, and shall so report to the Congress."