A great deal is known about the psychological profiles of liberals and conservatives, but very little is known about libertarians – an increasingly important group in the U.S. electorate. In this talk I’ll present the results of the largest and most comprehensive survey ever done of the psychological traits of libertarians. Nearly 12,000 self-identified libertarians completed one or more of 16 surveys at www.YourMorals.org. Compared to self-identified liberals (n = 97,021) and conservatives (n = 17,541), libertarians showed 1) stronger endorsement of individual liberty as their foremost guiding principle, and weaker endorsement of all other moral principles; 2) a relatively cerebral as opposed to emotional cognitive style; and 3) lower interdependence and social relatedness. These findings accord well with what libertarians say about themselves. I’ll show that they also fit well with a multi-level developmental model of personality (e.g., from Dan McAdams) in which innate temperamental factors influence but do not determine moral and political development, leading people to gravitate to some ideological narratives rather than others.