Frailty is prevalent in older adults with heart failure (HF), which increases their risk for basic and instrumental activities of daily living (ADL/IADL) disability and a diminished quality of life (QOL). However, the issue of conceptualizing frailty remains unresolved. To date, the two predominant frailty models are the Fried model, which defines frailty as purely physical, and the Gobben model, which defines frailty as multi-domain with physical, psychological, and social domains. An integrative literature review of frailty components in existing frailty measures was conducted. The most commonly used frailty components were mobility and balance, nutrition, and cognitive function. Next, a cross-sectional, secondary data analysis was conducted using data from the Health and Retirement Study (HRS) to compare the capacity of the Fried model and the Gobbens model to predict ADL/IADL disability and QOL. Compared to the Fried physical frailty model, the inclusion of psychological components from the Gobbens model significantly increased the power to predict ADL/IADL disability, while the psychological and social components from the Gobbens’ model significantly increased the ability to predict QOL. These findings support the view that frailty is a multidimensional syndrome with three domains (physical, psychological, and social). The levels of the three frailty domains were then compared, and older adults with HF were found to have higher levels of frailty across all three domains compared to older adults without HF.Lastly, a longitudinal examination of multidimensional frailty in older adults with HF was conducted, using HRS data collected at two time-points (2006/2008 to 2010/2012) from two cohorts. Across the two time-points, older adults with HF had higher levels of frailty across all three domains compared to older adults without HF. All HF and three frailty domains were associated with increased risks of ADL/IADL disability and decreased QOL. Each frailty domain mediated the relationship between HF and outcomes (ADL/IADL disability and QOL). The findings in this dissertation support frailty as a multidimensional syndrome. These findings have implications for the development of tailored, broad-based intervention aimed at preventing frailty or delaying its onset to reduce adverse outcomes of ADL/IADL disability and decreased QOL.