Pulmonary embolism (PE) is one of the big “can’t miss” diagnoses in the emergency department. Unfortunately, presenting symptoms are often vague, and definitive diagnostic testing is expensive and comes with risks of radiation and contrast to the patient. In order to avoid missing a PE while mitigating the risks associated with overtesting, some clinical decision tools have been created to aid in the diagnostic process. We will focus on two of these commonly used decision tools: the PERC rule and the WELLS score for PE.