The rate of surgical procedures in the older population is rising. Despite surgical, anaesthetic and medical advances, older surgical patients continue to suffer from adverse postoperative outcomes. Comorbidities and reduction in physiological reserve are consistently identified as major predictors of poor postoperative outcome in this population. Frailty can be defined as a lack of physiological reserve seen across multiple organ systems and is an independent predictor of mortality, morbidity and institutionalisation after surgery. Despite this identification of frailty as a significant predictor of adverse postoperative outcome, there is not yet a consensus on the definition of frailty or how best to assess and diagnose it. This review describes our current definitions of frailty and discusses the available methods of assessing frailty, the impact on the older surgical population and the emerging potential for modification of this important syndrome.