[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] "Man Up: Muscular Christianity and the Making of 20th-Century American Religion," examines the history of muscular Christianity in 20th-century America. Specifically, I analyze how liberal Protestants, Catholics, Mormons, fundamentalists, and evangelicals used muscular Christianity to navigate the cultural waters from religious outsiders into the mainstream. My project began by asking why millions of Americans hear sermons filled with sports analogies, attend Bible studies that follow a basketball game, and read books written by NFL quarterbacks? I discovered that over the course of the 20th century religious institutions, particularly religious colleges, used muscular Christianity to attract, convert, and retain men. By using student newspapers from Notre Dame, BYU and Wheaton College as a primary source base, my research provides a grassroots perspective on how the laity lived this religious message preached by religious authorities. I conclude that these communities used muscular Christianity to solidify their distinct religious identities and dissolve barriers with outsiders. Though its iterations shift over time and within each religious community, the blend of masculinity, sports, heroic-savagery, and homosocial community remained the remedy for the next generation to man up. My project expands the interpretation of 20th-century American history in three ways. First, I illustrate that muscular Christianity is one of the primary shapers of 20th-century American religion. Second my research explicates the larger cultural trends of therapeutic and consumer culture on American religion. Finally, my project helps fill the void in the history of religion and sports.