The prognosis of acute pulmonary embolism (PE) ranges from rapid symptom resolution to cardiovascular collapse and death. The Pulmonary Embolism Severity Index (PESI) is a rigorously derived and studied clinical prediction rule for PE prognosis that stratifies patients with acute PE into 5 classes (I-V) of increasing short-term overall mortality, based on 11 objective clinical variables readily available at the time of presentation. Numerous independent validation studies across the globe have demonstrated its accuracy and generalizability in identifying low-risk (class I-II) patients with PE who are potential candidates for less costly outpatient care. To facilitate the use of the PESI by busy clinicians, a simplified 6-variable version and auto-populating e-versions integrated into electronic health records have been developed and validated. Because of their methodological rigor, prognostic accuracy, and proven effectiveness and safety in both randomized and non-randomized controlled trials for managing low-risk patients in the outpatient setting, the original and simplified PESI (sPESI) have become reference standards for risk stratification of PE. Despite explicit guideline recommendations since 2014 to use the (s)PESI as a decision aid to identify low-risk patients with PE who are suitable for home care or early discharge, both the (s)PESI as well as outpatient management of low-risk patients remain largely underutilized.