This study explored the philanthropic landscape of professional athletes and their charitable foundations. This research also investigated factors influencing the formation of philanthropic foundations among this group of individuals. First, data were collected to identify athletes in four professional North American sport leagues who had formed charitable foundations. Then, 36 interviews were conducted with athletes, foundation directors, league and team executives and a sport agent to explore the motives and beliefs about philanthropy in professional sport. Using the theory of planned behavior, this paper identified the factors considered in the formation of charitable foundations in this unique group, primarily focusing on attitudes (altruistic and self-interested), perceived behavioral control, subjective norms, self-identity and moral obligation as antecedents to athlete philanthropic activity. The paper also discusses the unique context in which these individuals operate, some of the particular constraints they face, and identifies opportunities for athlete foundations and their partners.