For emergency physicians, acute pulmonary embolism (PE) provides a particularly complex diagnostic challenge. It has been estimated that 650,000 to 900,000 individuals annually suffer a fatal or nonfatal acute pulmonary embolism.1 While the classic textbook clinical presentation is well known, it is insufficiently accurate and precise in the timely diagnosis of an acute PE. In addition, many patients presenting with seemingly typical exacerbations of their underlying cardiopulmonary disease or other chronic illness may be masking symptoms of an undiagnosed acute pulmonary embolism.2 The high acuity coupled with the unreliable clinical presentation led to the development of several clinical tools, laboratory diagnostics, and radiographical studies to increase the clinician’s diagnostic power. This article we will review the Geneva Score and Wells Criteria, as well as the Kline and PERC rules. In addition, it will discuss special patient populations and diagnostic modalities for treating pulmonary emboli.