Chronic venous insufficiency (CVI) is an exceedingly common and underdiagnosed disorder with a wide range of symptoms and prognosis ranging from cosmetic issues to skin ulceration with tissue loss. Ultrasound plays a pivotal role in the diagnosis, classification, and guidance of percutaneous treatment of CVI. It is therefore of critical importance to the practicing radiologist to have a sound understanding of the pathophysiology, pertinent venous anatomy, and classification of CVI. We review the superficial and deep venous anatomy of the lower extremity, introduce a pattern recognition approach for mapping of varicosities, and review the protocol for ultrasound evaluation for CVI. In addition, we discuss the pathophysiology of CVI and the role of ultrasound in guidance for and follow-up of percutaneous treatment.