Pulmonary thromboembolism (PTE), a potentially dangerous condition, may present with various degrees of severity. A number of conditions are capable of producing venous thrombosis, which might subsequently lead to PTE. This chapter incorporates a practical and systematic approach for the diagnostic workup of a patient with suspected PTE. It explores the various presentations that should bring the condition to mind. The various predisposing conditions that need to be considered in the aetiological workup of venous thrombosis are examined. The pre-test probability of PTE is assessed in the context of the magnitude of risk involved. The role of D-dimer is examined in both outpatient and inpatient settings, and in conjunction with the clinical probability assessment score. The choice of imaging modality based on the merit of the test and potential contraindications is discussed in some detail.