Introduction: Chronic limb-threatening ischaemia (CLTI) is associated with high rates of mortality, major amputation, and functional decline. Frailty is increasingly used for risk stratification in vascular surgery, but its assessment in CLTI has not been systematically summarised. This review aimed to identify frailty instruments used in CLTI and evaluate their clinical utility. Results: Twenty-one studies met the inclusion criteria. Nine frailty instruments were identified, most commonly the Clinical Frailty Scale (8 studies), modified Frailty Index-5 (4 studies), and modified Frailty Index-11 (3 studies). Most studies were retrospective cohorts involving revascularisation, major amputation, or limb salvage. Mortality was the most frequently reported outcome (18 studies), followed by amputation or amputation-free survival (11 studies), functional outcomes (6 studies), readmission (5 studies), discharge disposition (5 studies), wound healing (2 studies), and frailty progression (2 studies). Higher frailty was consistently associated with increased mortality, worse amputation-free survival, poorer functional outcomes, and greater healthcare utilisation. CLTI-specific instruments, including the CLI Frailty Index and CLTI Frailty Risk Score, also demonstrated prognostic value. Conclusions: Frailty assessment demonstrates consistent prognostic value in CLTI across multiple clinically important outcomes. The Clinical Frailty Scale and modified Frailty Index were the most frequently used instruments, although several CLTI-specific tools have also been developed. Further prospective studies are needed to determine the optimal frailty instrument and assess whether frailty-guided decision-making improves patient outcomes.