In the future the number of frail independently living older people will continue to increase. It is unclear however, which people are meant exactly by those frail elderly. The aim of this article is to discuss the concept of frailty and its adequacy in identifying the frail elderly population. To this end, a literature search has been performed regarding the conceptual and operational definitions of frailty. The results show that frailty often is put on a continuum opposite to vitality. It is emphasised that the process of frailty can be modified or (partly) reversed. Focusing on this reversibility is important because frail elderly have a higher risk for adverse outcomes such as dependence, hospitalization, falls and mortality. After studying the conceptual and operational definitions it is concluded that no actual definition meets the criteria for a successful definition of frailty. Frailty is predominantly defined in terms of physical loss. This may lead to fragmentation of care with lack of an integral approach. In a follow-up study it will be tried to develop consensus on a conceptual and operational definition of frailty.