Diagnosis of pulmonary embolism (PE) has become based on diagnostic strategies based on clinical probability, that is, D-dimer measurement, lower extremity compressive ultrasonography, ventilation-perfusion scans, and for diagnosis helical computed tomography. Once a PE is identified, classification and clinical severity define treatment strategies. The American Heart Association (AHA) and European Society of Cardiology (ESC) have developed guidelines to classify PE severity. Furthermore, biomarkers have been identified to aid severity classification and treatment decisions. Biomarkers such as D-dimer, P-selectin, cardiac troponins, NT-proBNP, BNP, and h-FABP have been examined for their potential utility in PE prognostication and management. However, limiting biomarker use has been the lack of study into their utility and development of specific cutoffs for classification. This chapter will explore PE risk stratification guidelines, biomarkers of interest, and imaging-based markers to classify PE severity to guide treatment decisions.