Joseph Marion ("Jay") Tanner (March 26, 1859 – August 19, 1927) was an American educator and a leader in The Church of Jesus Christ of Latter-day Saints (LDS Church). He has been described as "one of the most gifted teachers and writers in the [LDS] Church in the late nineteenth and early twentieth centuries".
Tanner was born in Payson, Utah Territory in a Latter-day Saint family. He attended Brigham Young Academy in Provo, Utah before departing the United States as a missionary for the LDS Church. From 1884 to 1887, he preached Mormonism in Europe and the Middle East. Along with Jacob Spori, he was the first LDS Church missionary to preach in Turkey—where they baptized Mischa Markow—and was the organizer of the first branch of the LDS Church in Palestine.
From 1887 to 1891, Tanner was the principal of Brigham Young College in Logan, Utah. In 1891, he became the leader of the first group of Latter-day Saints to enroll at Harvard University. Tanner studied law at Harvard Law School until 1894, when his ill health prompted him to return to Utah.
From 1896 to 1900, Tanner was president of Utah Agricultural College, which is today Utah State University.