**1. Introduction**

The concept of frailty is frequently mentioned in studies related to the elderly population—health status, self-care dependence, healthcare resources or even the configuration of the wards where care is provided. Looking at the scientific knowledge and clinical practice, frailty in the elderly is considered a relevant dimension of quality of life. Moreover, there is a tendency to accept that individuals with severe frailty have to be considered vulnerable and should be protected.

Frailty has been viewed as a cornerstone of geriatric medicine and a platform of biological vulnerability to a host of other geriatric syndromes and adverse health outcomes [1], such as long-term nursing home stay, injurious falls and death, in community-dwelling older adults independent of medical comorbidities and age. The expression "frailty elderly" was used for the first time in 1970, by researchers from the Federal Council on Aging (FCA) of the United States, with the purpose of describing elderly people who lived in unfavourable socioeconomic conditions and presented physical weakness and cognitive deficit that, with advancing age, began to demand more care; in the 1980s, frailty in the elderly people was understood

mainly as synonymous of disability or the presence of a disease, chronic or extreme condition linked with ageing [2]. In 1990, the expression "frailty elderly" was referred for the first time on the *Journal of the American Geriatrics Society* index [2].

The term "frailty" started to be used frequently in terms of diagnosis, clinical decisions and provision of care. Frailty and cognitive and functional decline are relatively common in older dependent people with health problems. One of the challenges for researchers today has been to study the physical characteristics and psychological symptoms of frailty and to relate them to adverse health outcomes. In this chapter, we intend to analyse the matters that have most attracted the attention of researchers and health professionals who deal with people in situations of frailty.

Understanding frailty has become crucial for caring for the elderly. In older people with dementia, the assessment of frailty is more important than determining the degree of dementia, since it is crucial to develop appropriate care people need; there are old people with moderate dementia but with a severe level of frailty.

In this chapter, we intend to review the concepts of frailty, operationalization strategies and assessment tools and clarify some ideas from the debate on what frailty is.
