To become old means to become frail. The human body ages in ways that depend on genes, environmental-, and chance-factors, but if we do not end our lives as a result of a deadly accident or sudden onset of a lethal disease, we will all face a final phase of frailty before we die. Frailty may be caused by way of disease processes, but it can also consist in an increased sense of fragility, weakness, fatigue, and dizziness without a detected disease, which makes a person more likely to fall ill and make it harder to recover from illness. Neither phenomenologists nor existentialists have spent much time analysing frailty, except, perhaps, in the latter case, as a feature of human life to be avoided and resisted by way of a strong will and brave choices. The primary example would be Jean-Paul Sartre, but also Simone de Beauvoir is guilty of a certain contempt for bodily fragility. Arguably, the theories of some phenomenologists, such as Emmanuel Levinas and Paul Ricoeur, do a good job of rehabilitating human vulnerability in general, but not in the sense of a specific frailty related to illness and ageing. Despite this lack of a phenomenology of frailty in phenomenological-existentialist philosophy there are resources in this tradition to be exploited in developing such a subject. A phenomenology of frailty could be of importance not only for philosophers and empirical researchers, but also for old people and their care takers in attempts to make frail lives more bearable. The chapter develops a phenomenology of frailty by making use of concepts and arguments developed by existentialist thinkers, but also by scrutinizing them further and turning them against their fathers and mothers.