This document provides a comprehensive overview of the standardization of lung volume measurements, focusing on absolute lung volumes such as residual volume (RV), functional residual capacity (FRC), and total lung capacity (TLC). It integrates recommendations from the American Thoracic Society (ATS) and European Respiratory Society Task Force on pulmonary function standards, as well as earlier National Heart, Lung, and Blood Institute (NHLBI) workshops. The document covers various techniques for measuring lung volumes, including body plethysmography, nitrogen washout, gas dilution, and radiographic imaging methods. Key definitions and subdivisions of lung volumes are discussed, along with detailed guidelines for patient preparation, measurement techniques, quality control, and calculations. The document also addresses the limitations and advantages of different measurement methods, emphasizing the importance of accurate and reproducible results in clinical practice. Additionally, it highlights the role of lung volume measurements in assessing disease severity, functional disability, and response to treatment, particularly in infants, children, and adults.This document provides a comprehensive overview of the standardization of lung volume measurements, focusing on absolute lung volumes such as residual volume (RV), functional residual capacity (FRC), and total lung capacity (TLC). It integrates recommendations from the American Thoracic Society (ATS) and European Respiratory Society Task Force on pulmonary function standards, as well as earlier National Heart, Lung, and Blood Institute (NHLBI) workshops. The document covers various techniques for measuring lung volumes, including body plethysmography, nitrogen washout, gas dilution, and radiographic imaging methods. Key definitions and subdivisions of lung volumes are discussed, along with detailed guidelines for patient preparation, measurement techniques, quality control, and calculations. The document also addresses the limitations and advantages of different measurement methods, emphasizing the importance of accurate and reproducible results in clinical practice. Additionally, it highlights the role of lung volume measurements in assessing disease severity, functional disability, and response to treatment, particularly in infants, children, and adults.