Fatigue is a common symptom in idiopathic inflammatory myopathies (IIMs), which greatly affects activities of daily life. Fatigue is a complex phenomenon that covers a range of dimensions from biological to behavioural, the pathophysiology of which is still poorly understood. The aim of this review is to describe the different determinants of fatigue in IIMs, discuss their clinical implications and how to evaluate and manage the condition, which are all relevant issues for the treating physicians in their everyday practice.