This Element offers seven propositions toward a theory of 'Our Urban Planet' that is useful to global urban historians. I argue that historians have much to offer to theorists particularly those involved in debates over planetary urbanization theory and the Anthropocene. We must enlarge our concept of 'urban' to include spaces that make cities possible and that cities make possible and become comfortable with longer temporal frames that nest global urban history within Earth Time. Above all we need to add the crucial dimension of power, redefining cities as spaces that humans produce to amplify harvests of geo-solar energy and deploy human power within space and time. The element uses insights from 'deep history' to set the stage for a 'theory by verb' elaborating the many paradoxes of humans' 6,000-year gamble with the Urban Condition and explaining cities' own intrinsic capacity to outrun their own theorizability.