Expressed emotion (EE) is a measure of the family environment that predicts worse clinical outcomes for patients with a range of disorders. This article describes the assessment of EE and the evidence linking EE to clinical relapse in patients with psychopathology. This is followed by consideration of the possible explanatory models that might account for the EE-relapse link and a review of the evidence suggesting that EE may play a causal role in the relapse process. The results of studies describing the effect of EE on patients, as well as cross-cultural aspects of the construct, are highlighted. Finally, the possibility that high levels of EE may stress patients by perturbing activity in neural circuits that underlie psychopathology is considered and new directions for EE research are outlined.