Pulmonary embolism (PE) is the third most common cause of cardiovascular death worldwide, behind myocardial infarction and stroke. Due to pulmonary bed obstruction, PE can result in acute right ventricular (RV) failure which is a life-threatening condition. Because most patients ultimately die within the first hours of presentation, early diagnosis is very  important (1). Mortality due to pulmonary embolism varies greatly, depending on various factors including age, comorbid conditions, and stability on presentation. Patients with low-risk PE have a 1-year survival rate over 95%. In contrast, patients presenting with high risk PE and hemodynamic instability have an approximately 40% mortality rate within 90-days. In this review, we will discuss the basic pathophysiology of PE, risk factors for developing PE, and standard diagnostic testing modalities. We will also cover risk stratification of patients presenting with PE and the implications for treatment and disposition. While no exact epidemiological data are available, the incidence of PE is estimated to be approximately 60 to 70 per 100,000, and that of venous thrombosis approximately 124 per 100,000 of the general population (2). The European guidelines for the diagnosis and management of PE report annual incidence rates of venous thrombosis and PE of approximately 0.5 to 1.0 per 1000 inhabitants (3). However, the actual figures are likely to be substantially higher because silent PE can develop in up to 40% to 50% of patients with deep vein thrombosis (DVT) (3)