Frailty is a multifactorial medical syndrome characterized by reduced endurance and decreased physiological ability. The aim of this narrative literature review is to present the frailty diagnostic instruments that are already used in most Western countries and provide recommendations for use in clinical practice. Among the numerous available frailty instruments identified in current literature, the Frailty Index and the Physical Frailty Phenotype are most commonly used. There are large differences in each instrument design, ease of use by healthcare teams and also significant heterogeneity in the design of the studies based on these instruments. Therefore, future studies should be designed to properly address the discrepancy in the comparison of the existent instruments and consider their validity and feasibility of implementation in different healthcare settings with different healthcare providers.