The COVID-19 Resource Centre, established by Elsevier in January 2020, provides free information in English and Mandarin on the novel coronavirus. The centre is hosted on Elsevier Connect and grants permission for all related research to be made available in PubMed Central and other public repositories, with unrestricted reuse and analysis rights. The review aims to establish a standardized clinical case definition for post-COVID-19 condition, addressing the lack of standardized nomenclature and clinical definitions. The study employs a Delphi consensus method, involving a diverse group of experts, patients, and stakeholders from various WHO regions and income levels. The primary objective is to achieve consensus on the importance of variables and values in the definition. - **Participants**: 265 respondents in round one and 195 in round two. - **Domains**: 12 domains were identified, with three excluded and one added based on participant feedback. - **Variables**: 45 items were defined, including new symptoms, minimum time period from onset of COVID-19 to symptom presence, and duration of symptoms. Post-COVID-19 condition occurs in individuals with a history of probable or confirmed SARS-CoV-2 infection, typically 3 months after the onset of COVID-19, with symptoms lasting at least 2 months that cannot be explained by an alternative diagnosis. Common symptoms include fatigue, shortness of breath, and cognitive dysfunction, impacting everyday functioning. Symptoms may be new or persist from the initial illness and can fluctuate or relapse over time. - **Strengths**: Robust protocol-based Delphi method, inclusive and diverse participant representation. - **Limitations**: Limited response rates, underrepresentation of older participants, and subjectivity in symptom assessment. The definition is intended for community and healthcare settings to optimize recognition and care. It is likely to evolve as new evidence emerges and understanding of COVID-19's consequences continues to advance. The study acknowledges the ongoing challenges and uncertainties surrounding COVID-19 and its sequelae.The COVID-19 Resource Centre, established by Elsevier in January 2020, provides free information in English and Mandarin on the novel coronavirus. The centre is hosted on Elsevier Connect and grants permission for all related research to be made available in PubMed Central and other public repositories, with unrestricted reuse and analysis rights. The review aims to establish a standardized clinical case definition for post-COVID-19 condition, addressing the lack of standardized nomenclature and clinical definitions. The study employs a Delphi consensus method, involving a diverse group of experts, patients, and stakeholders from various WHO regions and income levels. The primary objective is to achieve consensus on the importance of variables and values in the definition. - **Participants**: 265 respondents in round one and 195 in round two. - **Domains**: 12 domains were identified, with three excluded and one added based on participant feedback. - **Variables**: 45 items were defined, including new symptoms, minimum time period from onset of COVID-19 to symptom presence, and duration of symptoms. Post-COVID-19 condition occurs in individuals with a history of probable or confirmed SARS-CoV-2 infection, typically 3 months after the onset of COVID-19, with symptoms lasting at least 2 months that cannot be explained by an alternative diagnosis. Common symptoms include fatigue, shortness of breath, and cognitive dysfunction, impacting everyday functioning. Symptoms may be new or persist from the initial illness and can fluctuate or relapse over time. - **Strengths**: Robust protocol-based Delphi method, inclusive and diverse participant representation. - **Limitations**: Limited response rates, underrepresentation of older participants, and subjectivity in symptom assessment. The definition is intended for community and healthcare settings to optimize recognition and care. It is likely to evolve as new evidence emerges and understanding of COVID-19's consequences continues to advance. The study acknowledges the ongoing challenges and uncertainties surrounding COVID-19 and its sequelae.