Scholars of medical history have discovered that the notion of “monstrous births” presented challenging legal issues in the early modern world. Were such offspring–often conjoined twins– “monsters” in the civil sense? Were they, for example, able to make a will, inherit, contract, and perform other civil actions? While the question of the “civil rights” of conjoined twins in the early modern period usually remained truly academic (as few such births survived), a whole series of other conditions–some unusual, some very common–raised similar medico-legal issues. Pregnancy, mental retardation, epilepsy, deformity, disputed sexuality (hermaphroditism, intersexuality, or castration), deafness, blindness, and even more fleeting circumstances such as fever, could call into question an individual's ability to perform normal legal actions or to be allowed to inherit an estate, serve as a guardian, or give testimony in court. This article examines how competence imperatives worked out in quotidian practice. While there are numerous points at which a “body” became problematic (in a medico-legal sense), this study uses two particular situations–baptism and marriage–to probe how practices were shaped not only by “experts” (physicians, theologians, and jurists) but also by what may be called local knowledge.