This consensus document provides an updated overview of the methods available for investigating chronic venous insufficiency (CVI) of the lower limbs, including their history, usefulness, and limitations. CVI is characterized by symptoms or signs resulting from venous hypertension due to structural or functional abnormalities of veins. The most common causes are primary abnormalities of the venous wall and valves, as well as secondary changes due to previous venous thrombosis. Due to the complexity of diagnosing CVI, various diagnostic investigations have been developed to assess calf muscle pump dysfunction and determine the extent and severity of obstruction or reflux. The document aims to guide clinicians in selecting appropriate tests for patients and interpreting results, covering both clinical and research applications. It highlights the importance of duplex scanning, which has become a valuable tool for monitoring thrombus evolution and detecting reflux after acute deep vein thrombosis (DVT). The document also discusses other methods such as phlebography, varicography, duplex scanning, ambulatory venous pressure (AVP) measurements, and photoplethysmography (PPG), each with its own advantages and limitations. The aim is to provide a comprehensive guide for both clinical practice and research in the field of CVI.This consensus document provides an updated overview of the methods available for investigating chronic venous insufficiency (CVI) of the lower limbs, including their history, usefulness, and limitations. CVI is characterized by symptoms or signs resulting from venous hypertension due to structural or functional abnormalities of veins. The most common causes are primary abnormalities of the venous wall and valves, as well as secondary changes due to previous venous thrombosis. Due to the complexity of diagnosing CVI, various diagnostic investigations have been developed to assess calf muscle pump dysfunction and determine the extent and severity of obstruction or reflux. The document aims to guide clinicians in selecting appropriate tests for patients and interpreting results, covering both clinical and research applications. It highlights the importance of duplex scanning, which has become a valuable tool for monitoring thrombus evolution and detecting reflux after acute deep vein thrombosis (DVT). The document also discusses other methods such as phlebography, varicography, duplex scanning, ambulatory venous pressure (AVP) measurements, and photoplethysmography (PPG), each with its own advantages and limitations. The aim is to provide a comprehensive guide for both clinical practice and research in the field of CVI.