The Edmonton Symptom Assessment System (ESAS) has been proposed as one element of a distress screening strategy in cancer patients. It consists of 11-point numerical rating scales for self-report of nine common symptoms of cancer, with a 10th scale for a patient-specific symptom. The ESAS has undergone widespread adoption internationally for clinical, research and administrative purposes. Despite its rapid uptake, validity evidence has lagged behind, and concerns have been raised about feasibility and usefulness. The objective of this paper is to provide a synthesis of a program of research focusing on the psychometric properties of the ESAS.