In this article, we discuss the approach for diagnosing deep vein thrombosis (DVT) in different patient populations. Clinical features and probability assessment guide further diagnostic tests. D-dimer testing is used as screening test; however, duplex ultrasound remains the primary confirmatory test. Computed tomography and magnetic resonance imaging are used only in select patient populations, such as when ultrasound results are equivocal, in patients suspected of central venous DVT, or as a part of combined protocol for diagnosis of pulmonary embolism. Contrast phlebography and plethysmography do not have much of a role during routine diagnosis of DVT.