An operational definition of frailty is important for clinical care, research, and policy planning. The literature on the clinical definitions, screening tools, and severity measures of frailty were systematically reviewed as part of the Canadian Initiative on Frailty and Aging. Searches of MEDLINE from 1997 to 2009 were conducted, and reference lists of retrieved articles were pearled, to identify articles published in English and French on the identification of frailty in community-dwelling people aged 65 and older. Two independent reviewers extracted descriptive information on study populations, frailty criteria, and outcomes from the selected papers, and quality rankings were assigned. Of 4,334 articles retrieved from the searches and 70 articles retrieved from the pearling, 22 met study inclusion criteria. In the 22 articles, physical function, gait speed, and cognition were the most commonly used identifying components of frailty, and death, disability, and institutionalization were common outcomes. The prevalence of frailty ranged from 5% to 58%. Despite significant work over the past decade, a clear consensus definition of frailty does not emerge from the literature. The definition and outcomes that best suit the unique needs of the researchers, clinicians, or policy-makers conducting the screening determine the choice of a screening tool for frailty. Important areas for further research include whether disability should be considered a component or an outcome of frailty. In addition, the role of cognitive and mood elements in the frailty construct requires further clarification.