Clinical discourses of frailty are central both to the construction of the social category of the fourth age and to the role and identity of hospital geriatric medicine. However, the influence of such clinical discourses is not just from science to the social sphere and nor do these discourses have their source in a putative truth of the old body but emerge from an interplay between physiological facts, discourses of governmentality, productive processes associated with late modern capitalism and the professional ambitions of geriatric medicine. The article explores this interplay in the two key discourses of frailty that have emerged in the clinical literature during the past 15 years, that of the phenotype and the accumulation of deficits, respectively. Outlining the development of the discourse of senescence from its origins to the more recent emergence of a nosological category of frailty the article explores how these key discourses capture the older body according to particular sets of norms. These norms link physiological understanding with broader discourses of governmentality, including the professional project of geriatric medicine. In particular, metaphorical representations in the discourses of frailty convey key cultural and clinical assumptions concerning both older bodies and old age more generally.