Venous thromboembolism (VTE) encompasses deep vein thrombosis (DVT) and pulmonary embolism (PE) as manifestations of the same pathological process. Virchow's triad defines the three etiological factors: venous stasis (immobilization, surgery, heart failure), endothelial injury (trauma, surgery, central lines), and hypercoagulability (inherited thrombophilia, cancer, pregnancy, OCP use). Diagnosis follows validated clinical decision algorithms. DVT Wells Score: active cancer (+1), paralysis/immobilization (+1), bedridden >3 days or surgery within 12 weeks (+1), localized tenderness along deep veins (+1), entire leg swollen (+1), calf swelling >3 cm vs asymptomatic leg (+1), pitting edema (+1), collateral superficial veins (+1), previously documented DVT (+1), alternative diagnosis as likely as DVT (-2). Score interpretation: ≤1 = DVT unlikely (proceed with D-dimer; if negative, DVT excluded); ≥2 = DVT likely (proceed directly to compression ultrasonography). PE Wells Score: clinical signs of DVT (+3), PE most likely diagnosis (+3), heart rate >100 (+1.5), immobilization/surgery within 4 weeks (+1.5), previous DVT/PE (+1.5), hemoptysis (+1), malignancy (+1). Score >4 = PE likely (proceed to CTPA); ≤4 = PE unlikely (D-dimer first). Age-adjusted D-dimer cutoff (age × 10 mcg/L for patients >50)...