Objective: To describe the epidemiology of sepsis in critical care by applying the Sepsis-3 criteria to electronic health records. Design: Retrospective cohort study using electronic health records. Setting: Ten intensive care units (ICU) from four United Kingdom National Health Service hospital trusts contributing to the National Institute for Health Research Critical Care Health Informatics Collaborative (CC-HIC).Patients: 28,456 critical care admissions (14,332 emergency medical, 4,585 emergency surgical, and 9,539 elective surgical)Measurements and Main Results: 29,343 episodes of clinical deterioration were identified with a rise in Sequential Organ Failure Assessment (SOFA) score of at least 2 points, of which 14,869 (50.7%) were associated with antibiotic escalation and thereby met the Sepsis-3 criteria for sepsis. 4,100 episodes of sepsis (27.6%) were associated with vasopressor use and lactate > 2.0 mmol/l, and therefore met the Sepsis-3 criteria for septic shock. ICU mortality by source of sepsis was highest for ICU-acquired sepsis (23.7%, 95% CI 21.9%, 25.6%), followed by hospital-acquired sepsis (18.6%, 95% CI 17.5%, 19.9%), and community-acquired sepsis (12.9%, 95% CI 12.1%, 13.6%) (p for comparison