This chapter introduces the phenomenon of personal parishes in contemporary American Catholicism. Personal parishes organize Catholics on the basis of purpose rather than territory. They cluster local Catholics by ethnicity, liturgical preference (including for the Traditional Latin Mass), social justice orientation, and more. In making room for diverse expressions of Catholicism, personal parishes represent a structural response to heterogeneity from the top. Their patterns of use over time showcase organizational changes to how bishops structure local Catholicism. National parishes were once commonplace; today, a growing number of dioceses introduce personal parishes for new purposes. This chapter previews the remaining content of the book as well as briefly summarizing the mixed methodological approach upon which this research is based.