Pulmonary embolism often, but not exclusively, originates from lower extremity veins with DVT. Ultrasound has largely replaced contrast venography because of its ease, wide availability, and accuracy (particularly for femoropopliteal DVT). The modern US protocol includes grayscale imaging, Doppler waveforms, and color Doppler to assess vein compressibility, flow characteristics, and luminal filling. Compression ultrasound detects thrombosis and can generally differentiate acute thrombus from post thrombotic changes. Spectral Doppler evaluates waveforms for obstruction or reflux. In clinical practice, comprehensive ultrasound from inguinal ligament to ankle aids in thorough evaluation, crucial for accurate diagnosis and management planning. Ultrasound is essential in patients suspected of PE but lacking immediate access to other chest imaging. Moreover, ultrasound plays a role post-PE diagnosis, assessing for residual DVT that may alter treatment strategies and predict outcomes such as post-thrombotic syndrome. Research is ongoing to determine the role of residual DVT as a risk factor for morbidity and mortality.