This article discusses the standardization of lung function testing (PFTs) and provides guidance on interpreting PFT results. It outlines the importance of using reference equations derived from healthy populations to ensure accurate interpretation of spirometry, lung volumes, and diffusing capacity for carbon monoxide (DL,CO). The article emphasizes the need for quality control in PFT interpretation, including reviewing test quality and comparing results with reference values. It also highlights the importance of considering factors such as age, sex, ethnicity, and height when selecting reference equations. The article discusses the use of reference equations for different age groups and ethnicities, and notes that some populations may require adjustment factors for accurate interpretation. It also addresses the interpretation of changes in lung function and the classification of severity based on FEV1% predicted. The article provides recommendations for the use of bronchodilator response tests and discusses the importance of considering clinical context when interpreting PFT results. The article concludes with a summary of the considerations for severity classification and the importance of using appropriate reference equations for accurate interpretation of lung function tests.This article discusses the standardization of lung function testing (PFTs) and provides guidance on interpreting PFT results. It outlines the importance of using reference equations derived from healthy populations to ensure accurate interpretation of spirometry, lung volumes, and diffusing capacity for carbon monoxide (DL,CO). The article emphasizes the need for quality control in PFT interpretation, including reviewing test quality and comparing results with reference values. It also highlights the importance of considering factors such as age, sex, ethnicity, and height when selecting reference equations. The article discusses the use of reference equations for different age groups and ethnicities, and notes that some populations may require adjustment factors for accurate interpretation. It also addresses the interpretation of changes in lung function and the classification of severity based on FEV1% predicted. The article provides recommendations for the use of bronchodilator response tests and discusses the importance of considering clinical context when interpreting PFT results. The article concludes with a summary of the considerations for severity classification and the importance of using appropriate reference equations for accurate interpretation of lung function tests.