--- - |2 Summary The most fundamental proposition of attraction–selection–attrition (ASA) theory is that organizations progress toward homogeneity of personality over time through the processes of attraction, selection, and attrition. However, critical aspects of that proposition have remained untested, thus limiting a fuller understanding of the ASA theory. To close the gap, this multiwave, multisample, and multi‐inventory study examines the extent to which each of the ASA processes and different personality traits contribute to within‐organization homogeneity progression as well as between‐organization heterogeneity progression over time. Our findings suggest that both within‐organization homogeneity and between‐organization heterogeneity emerge to varying degrees over time and that selection, among the ASA processes, is most responsible for the within‐organization homogenization, whereas attraction contributes most to between‐organization heterogeneity. We also found that within‐organization homogeneity progression overall operates more strongly on extraversion than on the other personality traits, whereas between‐organization heterogeneity progression operates more strongly on neuroticism than on the other personality traits. Overall, this study provides an important extension to the ASA theory and useful insights into the organization‐level emergent process of personality‐based human capital resources. We discuss theoretical and practical implications of this study along with study limitations and future research directions. - Journal of Organizational Behavior, EarlyView.