The present paper aims at reviewing our present knowledge on the diagnosis of deep vein thrombosis and pulmonary embolism with a particular emphasis on clinically suspected outpatients. The various contemporary diagnostic tools (including clinical probability assessment, fibrin D-Dimer measurement, venous compression ultrasonography, ventilation/perfusion lung scintigraphy, helical CT scan, and echocardiography) are presented and rational sequential strategies are discussed in their various aspects, including validation in outcome studies, and cost-effectiveness analyses.