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 <0.0001).Conclusions: We successfully operationalized the Sepsis-3 criteria to an electronic health record dataset to describe the characteristics of critical care patients with sepsis. This may facilitate sepsis research using electronic health record data at scale without relying on human coding.