William Pierce Frye (September 2, 1830 – August 8, 1911) was an American politician from Maine. A member of the Republican Party, Frye spent most of his political career as a legislator, serving in the Maine House of Representatives and then U.S. House of Representatives, before being elected to the U.S. Senate, where he served for 30 years before dying in office. Frye was a member of the Frye political family, and was the grandfather of Wallace H. White, Jr., and the son of John March Frye. He was also a prominent member of the Peucinian Society tradition.

Fry was a leader of the "Old Guard" faction of conservative Republicans, exerting his weight on such important committees as Rules, Foreign Relations, Appropriations, and Commerce. He was best known for supporting the shipping industry, but repeatedly failed to obtain government subsidies. He also supported high tariffs, expansion that sought additional territory and the canal connecting the Atlantic and Pacific. He favored the annexation of Hawaii and the acquisition of the Philippine Islands in 1898. President William McKinley appointed him to the peace commission it negotiated the end of the Spanish-American war.