Australia’s total number of pathology tests and imaging services covered by the Medicare Benefits Schedule has increased by over 50% in the last decade. Given that 20-25% of the common pathology tests were considered inappropriate nationwide, an increasing burden is being placed on the whole healthcare system by unnecessary diagnostic tests (UDTs). The objective of this exploratory study is to identify the contextual factors that could influence a clinician’s diagnostic test ordering decision-making (DTODM) in an Emergency Department (ED). Semi-structured interviews were conducted with 19 ED clinicians. Four factors have been identified, including organizational context, patient/family preferences, resource availability, and influences by senior clinicians. The study offers new lenses in clinical reasoning for emergency medicine teaching and training through the eyes of ED clinicians. It also outlines an opportunity to introduce novel clinical decision support to assist with clinicians’ test ordering without causing alert fatigue or bringing stress.