Prominent models of personality structure posit that the patterning of thoughts, feelings, behaviors, and motivations can be universally captured by five or six relatively distinct dimensions. But mounting empirical work suggests personality structure varies across populations. What accounts for this variation? The niche diversity hypothesis proposes that personality structure arises from the affordances of unique trait combinations within a population. It predicts that personality traits will exhibit lower intercorrelations and greater variance in populations with more diverse niches. I will present an overview of previous research testing the niche diversity model of personality structure and discuss in-progress tests across nations, regions within Europe, and counties in the USA.