The Lyon Consensus on the diagnosis of GERD provides a comprehensive guide to modern diagnostic methods and criteria. It emphasizes that clinical history, questionnaire data, and response to antisecretory therapy are insufficient for a conclusive diagnosis of GERD alone but are valuable in determining the need for further investigation. Advanced evidence for reflux on oesophageal testing includes advanced grade erosive oesophagitis, long-segment Barrett’s mucosa, peptic strictures, or distal oesophageal acid exposure time (AET) >6% on ambulatory pH or pH-impedance monitoring. A normal endoscopy does not exclude GERD but provides supportive evidence when combined with distal AET <4% and <40 reflux episodes on pH-impedance monitoring off proton pump inhibitors (PPIs). Reflux-symptom association on ambulatory reflux monitoring adds supportive evidence for reflux-triggered symptoms and may predict better treatment outcomes. When endoscopy and pH or pH-impedance monitoring are inconclusive, adjunctive evidence from biopsy findings, motor evaluation, and novel impedance metrics can enhance confidence in the diagnosis of GERD. However, these findings alone are insufficient for a diagnosis. An assessment of anatomy, motor function, reflux burden, and symptomatic phenotype is essential for directing management. Future strategies should focus on defining individual patient phenotypes based on reflux exposure, mechanism, clearance efficacy, underlying anatomy, and psychometrics. The consensus aims to guide practitioners in making more accurate and informed decisions in the diagnosis and management of GERD.The Lyon Consensus on the diagnosis of GERD provides a comprehensive guide to modern diagnostic methods and criteria. It emphasizes that clinical history, questionnaire data, and response to antisecretory therapy are insufficient for a conclusive diagnosis of GERD alone but are valuable in determining the need for further investigation. Advanced evidence for reflux on oesophageal testing includes advanced grade erosive oesophagitis, long-segment Barrett’s mucosa, peptic strictures, or distal oesophageal acid exposure time (AET) >6% on ambulatory pH or pH-impedance monitoring. A normal endoscopy does not exclude GERD but provides supportive evidence when combined with distal AET <4% and <40 reflux episodes on pH-impedance monitoring off proton pump inhibitors (PPIs). Reflux-symptom association on ambulatory reflux monitoring adds supportive evidence for reflux-triggered symptoms and may predict better treatment outcomes. When endoscopy and pH or pH-impedance monitoring are inconclusive, adjunctive evidence from biopsy findings, motor evaluation, and novel impedance metrics can enhance confidence in the diagnosis of GERD. However, these findings alone are insufficient for a diagnosis. An assessment of anatomy, motor function, reflux burden, and symptomatic phenotype is essential for directing management. Future strategies should focus on defining individual patient phenotypes based on reflux exposure, mechanism, clearance efficacy, underlying anatomy, and psychometrics. The consensus aims to guide practitioners in making more accurate and informed decisions in the diagnosis and management of GERD.