Although Spanish colonizers expected horses to enforce social order, new environments for breeding and keeping horses and colonial interdependence on Indigenous populations also subverted these expectations. Licenses to ride horses offers a widespread example of this new political ecology. Across New Spain and Peru, Indigenous allies gained access to horses according to Spanish customs that rewarded military service to the crown, cases that emphasize the powerful imprint of the horse in Spanish governance. More broadly, the development of Indigenous equestrianisms both within and outside of Spanish spheres of influence demonstrate the complex boundary work involved in navigating a new interspecies landscape and producing new forms of knowledge.