Frailty is defined as a reduced physiologic reserve vulnerable to external stressors. For older individuals, frailty plays a decisive role in increasing adverse health outcomes in most clinical situations. Many tools or criteria have been introduced to define frailty in recent years, and the definition of frailty has gradually converged into several consensuses. Frail older adults often have multi-domain risk factors in terms of physical, psychological, and social health. Comprehensive geriatric assessment (CGA) is the process of identifying and quantifying frailty by examining various risky domains and body functions, which is the basis for geriatric medicine and research. CGA provides physicians with information on the reversible area of frailty and the leading cause of deterioration in frail older adults. Therefore frailty assessment based on understanding CGA and its relationship with frailty, can help establish treatment strategies and intervention in frail older adults. This review article summarizes the recent consensus and evidence of frailty and CGA.