Background: Several studies show the effectiveness of face-to-face interventions with families in improving the prognosis of patients with severe psychiatric disorders and their relatives; however, the effectiveness of online interventions is poorly understood. The current study aims to provide an overview of evidence for the effectiveness of online treatments (web/app) for patients with severe psychiatric disorders and their families.; Method: We performed a systematic review of online treatments for informal family caregivers of patients with a severe psychiatric disorder. The study psychological interventions had to have been administered in an exclusively online format (app, internet) and aimed at families of patients with severe mental disorder (at least one of first episode psychosis, schizophrenia, schizoaffective, bipolar disorder, and psychotic disorder).; Results: Of a total of 1331 articles, we identified 9 viable studies; 4 randomized clinical trials, and 5 nonrandomized clinical studies. The present study is the first systematic review in this area. Online interventions were well accepted, with good adherence and satisfaction among the caregivers and patients and improved the symptoms of both caregivers and patients.; Limitations: Clinical and methodological diversity of the studies.; Conclusions: Burden improved, and perceived stress decreased in families. Moreover, the severity of positive symptoms decreased and fewer hospitalizations were recorded in patients than in the control group. Therefore, online interventions are a promising therapeutic approach for patients with severe mental disorder and their families. However, more studies-particularly randomized clinical trials-are needed in this area.