Fatigue is a sensation known to everyone. However, it is a concept that eludes universal definition or description; it varies in severity, intensity and frequency. This review was undertaken to articulate the constructs associated with fatigue, and to consider the high levels of fatigue reported in conditions where physiotherapists have an integral role in management and rehabilitation, such as multiple sclerosis and stroke. The prevalence of fatigue in the general population, and in those with co-morbidities will be presented. Fatigue has been researched extensively in multiple sclerosis and cancer; this is not the case in Parkinson's disease and stroke: nonetheless, fatigue is reported frequently in these populations. Methods of measurement of fatigue will be discussed, and treatment approaches reviewed. The current evidence suggests that fatigue is best measured using self-report instruments, and that treatment approaches should be informed by comprehensive assessment.